SNH:
But yeah there is already a ton of good stuff mentioned in this thread. already watched around 5 titles, would definitely recommend The River
If you liked it, you should check out the rest of Tsai Ming Liang's movies. Some of them are more provocative, some of them are pretty mild but most of them have the same set of actors and, watched in chronological (release date) order make some kind of prequel-sequel relation list (but not exactly, all of them can be watched separately), where Hsiao Kang/Lee Kang Sheng grows up - starts as a very unhappy teenager, then very unhappy young adult. If you like the kind of depressing, unhappy and suffocating atmosphere TML creates, I recommend you check out other movies from Taiwanese New Wave Cinema. For example Toon Wang's A Hill of no Return - maybe not the most taboo movie, but it depicts gloominess of life perfectly.
There's also https://mydramalist.com/51903-run-away - made by TW and TML duo. I haven't seen it personally but synopsis seems like you might enjoy it - and you also liked The River.
I just remembered I also watched a PH movie called Mondomanila: https://mydramalist.com/28175-mondomanila It's brutal, provocative, shot in a very unique way. It was very very disturbing.