After the recent upgrade to Fedora 34 from 33, my desktop PC doesn’t wake from standby, or from manually shutting down the screen with xset, except for the first 10 seconds. After, for like 2-3 min, I am still able to reboot using ALT Sysrq + B, but after this passes PC becomes completely unresponsive and I can only do a physical force shutdown.
I’m using KDE as DE, and my VGA is an AMD.
I googled and found this was a common problem in the past version, but before the upgrade it never happened. I also tried different kernel/mesa driver versions, but that didn’t help at all.
Just as a temporary workaround, you might add noacpi to your kernel command line so that your system doesn’t lock up if you are away/distracted for too long.