听说，我在报纸上看到一篇关于她的新闻，他现在已经是一个有名的作家了。
When should I not use 了?
It's especially strange because the 了 at the end means a change in state, right? But I have seen explanations that it also refers to some fact in the past. Unfortunately, very little is said about this.
听说，我在报纸上看到一篇关于她的新闻，他现在已经是一个有名的作家了
The sentence is incorrect, as 听(hear) and 看(see) represent two different senses, a conjunction is required to link them into one sentence,
Note that "了" is optional in this case, since the verb phrases "听说" and "看到" indicate the actions are/have been completed already. However, "了" is necessary to mean the action has been completed if you say,
A good/clear learning resource for 了1 and 了2 - https://resources.allsetlearning.com/chinese/grammar/Uses_of_%22le%22
You can use 了 after 看到 if you wish.
Something wrong with what you wrote, 听说 doesn't make sense if you say, “听说我在报纸上 ···” You must know whether or not you read the paper!
了 is hard to explain. I would compare that with trying to exhaustively explain to foreign learners of English when you must use "the" and when you may omit "the"
You will find many examples of 看到了：看到了吗？ and you may write your sentence with 了 or not：
我在报纸上看到了一篇关于她的新闻，...
and you may omit the last 了：
她现在已经是一个有名的作家。
Hard to find a simple, scientific, always applicable answer for this!
See, you must know first that 了 is maybe the most popular Chinese character ever. Basically, the character 了 is much more than just an indicator indicating that an action is completed.
First, the character 了 can be a part of some specific Chinese sentience structures. In such cases, the character 了 just act like a linguistic tool with completely no reference for any past action. The first fixed linguistic structure in which the character 了 is used in is whenever you use the Chinese character 太，here’s the exact sentence structure:
太 + adj. + 了
In this previous fixed structure, you first write the character 太, followed by any adjective, then the character 了 in order to reflect how strong this adjective. Here’s an example for this sentence structure:
太好了 (very good, extremely good)
Note that the character 太 means very, or extremely.
Another fixed case in which the Chinese character 了 is strongly used is when wanting to show exaggeration using the Chinese character 死，here’s the exact sentence structure:
adj. + 死 + 了
In this previous fixed structure, you first write whatever adjective you want, followed by atheism character 死, then the character 了 in order to reflect how strong this adjective really is. Here’s an example for this sentence structure:
我困死了 (I’m very tired, deadly tired)
Note that the character 困 means tired
Note that the character 死 originally means die, or death, but in such cases,
it just show exaggeration .
Second, the character 了 is representing that a specific action is over. Note that the character 了 is not representing past tense, it’s representing the concept of that a specific action is over. Don’t worry, I’ll clarify this point just now. When talking about the main usage of the character 了，we must first being reflected on how Chinese people look to the tense of any verb when using the character 了. we are talking here about a completely new unique perspective in which we’re not used to as English-Speakers.
In English Language, we just determine the tense of the verb according the the present moment, so if you said I went yesterday, that’s past, because it’s an action which has taken place before the current moment. on the other side, if you said I will go tomorrow, that’s future, because it’s an action which will take place in the future.
For a Chinese person, it’s a completely different story. Were whenever he talks about a verb, he travels in time to the moment in which the verb is happening in, whenever it is in the past, future, or present, then he see, in this moment, will the verb be over or no. If it will be over, he uses 了, even if this is at the future.
Since this concept is kind of complicated, here are two videos which will no sought help you have a full understanding of all the aspects of the Chinese character 了 https://youtu.be/5mnag_q--oU https://youtu.be/1A1laEwquPo
However, note that this character has got a lot of different uses, I don’t ant you to be confused. Watch the videos I lifted you up and enjoy your Chinese learning journey ^_^
Textbooks teach that a 了 after a verb is the "completion 了", which is correct, but they seldom mention that adding the 了 is often optional. I.e., even if a verb does not have a completion 了, it might still be completed. That's what's going on here.
If you go onto YouDao or some other example-sentence website, you'll see lots of examples of completed verbs without 了. Here's a few from this site (my translation):
我们分成几个搜索小组。 [We split into several search parties.] (no 了 after 分成)
政府方面昨天透露，削减可能势在必行。 [The government side revealed cuts are imperative.] (no 了 after 透露)
他下令开始工作。 [He ordered [sb.] to start work.] (no 了 after 下 in 下令)
This is very confusing for native-English speakers, because we would not think of tense in the same way: we generally cannot use present or future tense to describe something in the past---it's generally not optional in English. (Yes, 了 is not tense, but tense is the closest concept in English, so a lot of learners relate the two.)
If you compare native-Chinese writing to Chinese-as-a-second-language writing, the key giveaway is native-Chinese writing contains far fewer 了s.
The verbal suffix 到 can be used to convey 2 different meanings according to the context.
(A) The meaning of "manage to do something". For example:
In this kind of context, the process (i.e. "find the principal", "see the dog", "buy live fish") is presupposed to be associated with a goal. The use of 到 indicates that the goal has been attained (or not attained if used in negative form).
In a context of interlocution (or conversation) that involves a spekaer and a co-speaker, it is quite common (but not necessarily) to add the sentence particle 了 if the goal has been indeed attained：
1a. ... 我终于找到校长了。(We/You expected me to find the principal, and I assert to you that I did find him).
2a. ... 看到了，是只黄色的小狗。(We/You expected me to see the dog, and I assert to you that I do see it).
(B) The meaning of "it just so happens that...". For example:
In this kind of context, not only the process (i.e. "saw the princiapal", "received a parcel", "heard a piece of news”）is not associated with a goal, it cannot even be associated with an intention.
English speakers learning Chinese may want to take note of this: while the aspect marker 了 is used with many process to indicate that an individual occurence is located on the time plane (i.e. 我买了一辆车，他吃了两个三明治，她把窗关了），it is 到 but not 了 that we use when it comes to non-intentional processes like "see", "hear", "smell", "receive", etc.
To put it another way, if we use 了 with a process like these, the process must be interpreted as intentional:
I don't know who told you that 了 means "a change in state". Don't learn Chinese from him. S/He is simply cheating you.
了 means something (usually the thing you're talking in the sentence) have been done; it is completed. It has nothing to do with a change of something. Forget about the change.
You speak because you want to convey something to your listener or reader. So you use 了 or not wholly for that purpose. Remember.
Specifically, when you say "他现在已经是一个有名的作家了。", you are convey the idea to your listener or reader that "他现在已经是一个有名的作家" is a fact. It is something that has already taken place and that has already done. He is not trying to be a famous writer, he is not in the process of being a famous writer, but he has already been a famous writer, for example, by already publishing a top-sell novel. That's what you want to convey by taking pains to speak this Chinese.
If you don't use "了", that mean your sentence does not care whether this thing has already done. Taking the previous sentence as an example, if you say "我在报纸上看到了一篇关于她的新闻", you are confirming to your listener that you have really read it. This reading has happened, and you can't disguise that you didn't. Also, that you have read her news means that the news is true, it is not something still in rumor. Maybe "我在报纸上看到了飞机失事的新闻" can explain this better. That's a confirmation that an airplane really crashed.
But if you say "我在报纸上看到一篇关于她的新闻，" as in your question , you're not stressing that you have done a thing called reading her news, even if you really did it. This sentence is acting only as a preamble. What is important is the next sentence "他现在已经是一个有名的作家了". So, you don't need to use 了 in "我在报纸上看到一篇关于她的新闻" to stress that you read a piece of news. What matters is the contents of the news, which you would say immediately, and confirm it is done and completed by using 了 in that sentence.
To wrap up, remember that you are speaking to convey something, not just to pass an exam. Only by remembering this can you understand how to speak Chinese well (and all other foreign languages I think).
To add, since 了 means something has happened, the speaker can convey some emotion by stressing the pronunciation of 了. For example "我困死了" in another answer. This sentence is not only a confirmation that I am sleepy, but also an urge that I must go to bed now. Otherwise I would fall asleep on the table immediately, say. So, the key is the conveyance of information in your sentence. That's always why you speak.
