I have a i7-9700K + RTX 2080 8Gb GDDR6 + 32Gb RAM DDR4.
And I really think it is not a bad desktop, however I have been noticing that when I am playing Doom Eternal or Far Cry 4 (and even happened during a Spires of Ascension run on last boss) the GPU temperatures really go up (HWiNFO64 reports 80-90º) as also its fans (reached the 4k RPM mark, with an average of 2,3k RPM).
I have opened the case and cleaned every fan on it as also removed the GPU and cleaned every single fan.
You can limit FPS to the refresh rate of your display so that so the GPU isn’t doing 100 or 200 FPS when the screen can do 60Hz or some higher set value.
Then there is case airflow. If the case is bad at airflow hot air will stay in the case.
feel like you should never reach 90c under normal circumstances, you should hit a temp limit around 81 or 84 or something and it should throttle hard to maintain that. you changed the temp target maybe?
gpu temps in the 80s is normal for the less powerful air coolers anyway, 90’s a bit high.
also try undervolting, can probably drop power a considerable amount without dropping performance.
try removing case panels to see if you have an airflow problem.
think about doing a paste swap if your card is from a manufacturer who won’t fight you on warranty if you do.