I guess this word means a term of an official post, but now we also find words like 这一届网友不吃你这一套 or 这一届群众没那么容易欺骗了，so what does the word really mean? 今年举办的欧洲杯是第几届？what exactly does that mean? Does it mean how many matches will be held for the EUFA Cup this year?
～屆 is a counter for regularly/periodically held events. More formal than
～次, one may say.
第十六屆歐洲盃 the sixteenth EUFA cup
本屆理事 incumbent director
It is however used figuratively in
這一屆網友. I guess one may translate that into 'this generation of netizens'. Generations (of netizens) do come and go.
In mainland China 这一届网友/人民 is mostly a mocking phrase that was inspired by 这一届政府(this term of government office, a formal description).
Typical usages I've seen:
- "这一届人民不行" —— First happened as a self mockery. There was an official media article saying that the people should be blamed for social corruption. People replied "这届人民不行，配不上这届政府".
- "这届网友不行" —— Again mockery, millennials criticizing post-millennials for being more conservative and more nationalist.
Your examples seem to be from the post-millennial generation. They seem to use 这届 differently. I don't see mockery in these examples. Also note that both these examples have nationalist connotations.
- 这一届网友不吃你这一套 (Mind your attitude. We're not to be trifled with)
- 这一届群众没那么容易欺骗了 (Go away with your western propagandas)
"今年举办的欧洲杯是第几届？" is certainly not asking how many matches. It's asking something that is hard to express directly in English. If I had to ask such a thing in English I would say "What season number was this year's UEFA Europa League season?" I believe the answer is "The 51st season." The 2021–22 UEFA Europa League was the 51st season of Europe's secondary club football tournament organised by UEFA, and the 13th season since it was renamed from the UEFA Cup to the UEFA Europa League.
You could similarly have asked "今年举办的奥运会是第几届？" which would be "This year's Olympics were the games of which Olympiad?" for which the answer last year was "The 32nd Olympiad."
届/屆 represent for the whole process of an event or an activity, like the term of a president, a national congress, a sports meeting, the students of a school year, etc.
It is an internet slang, 一届网友/一屆網友 refers to a generation of netizen whose thoughts or opinions changed greatly against those in previous years or decades.