I had this exact same problem when I switched from windows to fedora KDE a couple months ago. The solution for me was to install the proprietary nvidia Linux drivers. The OS has some already bundled, but I found some other people online have this issue until they switched drivers and I gave shot. Im on my phone so I dont have any links or much else to give you rn, but if you need me to provide more info I can when I get back on my PC.

I had the same problem until I installed the nvidia drivers. KDE will install some that gets things to work but I had that sleeping problem you mention. I can’t remember the exact package name but I can try and figure it out if you need help finding it.