I guess it's my turn to give feedback in your thread now
I'm not going to patronize you & tell you to stop playing - It is the right answer, but it's clearly something you don't want to hear, so instead I'll try & offer some advice...
Firstly, before you play (especially if you're pushing yourself into RSI territory), consider following a routine like this:
https://www.youtube.com/watch?v=1XsLRQFV7rY
Stretching & massaging key hand muscles are the secret to keeping your hands fresh for longer periods of time. If I know I'm going to sit down & play guitar for a while, I'll be doing something along the lines of this video.
Secondly, even after that, don't just jump straight into osu! It's a very demanding game on the keyboard hand, so warm up with something else first, even if it's just typing to friends on Discord or whatever.
Other than that, just make sure you can get as naturally comfortable as possible before playing, and hey... Maybe try playing with the Relax mod once things get too bad? I tried it a bit yesterday - It's the only time I'll ever get 93% on Freedom Dive, I know that much >.<