Okay so..

I had some troubles with my computer for quite a long while ( journal ).
Thank you for the kind people who contacted me and gave me good tips!

I ended up simply trying to restore the C drive, and NOW it's finally back to normal
as it should be. It now has again over 30GB of free space, AS IT SHOULD.
Also my tablet and Clip Studio are working perfectly and the brushes aren't
wonky or blurry anymore, so probably the restoration fixed that issue as well! ♥

I'm hoping this'll last now, and won't be just a temporary fix. I'm still super nervous
every time I open my computer, but for now it's been two days of peace.
I'll slowly get back on track and finish some unfinished works, and finally
get working on the commissions I have.