In this statement, what is the function of 令？ and why is it not 對？ I was kinda expecting to see a “對” somewhere here.
令 has the meaning of "make"
You sing by my ear side everyday [make] me very depress
對 means "to"
You sing by my ear side everyday, [to] me is a kind of torture
You sing by my ear side everyday is a kind of torture [to] me
Notice: "令"(make) is a verb. "對" (to) is a preposition
令人 is a very common phrase.
令人：(used in conjunction with a verb) cause someone to (be, feel, etc)
令人不可思议 令人失望 令人出乎意料
You singing in my ear every day is making me depressed.
壓抑 is an adjective, so you can't use 對 here.
令 is followed by an adjective, eg壓抑
.... makes me depressed
你日日喺我耳邊唱歌 對我 ☓好壓抑 ✓造成好大困擾
對 is followed by a noun/phrase
... causes trouble to me