Did you check the task manager in the live system?
Also how high is the temperature of your cpu?
EDIT: If it crashed after the new installation and then runs so slowly maybe another new installation helps…
I don’t know what happened, but I decided to go all the way and use my grandfather’s old way. I turned off the power to the motherboard and let it “rest and think”, after that everything went back to normal. It has always helped, and it still helps) Most likely it was cosmic rays or the NSA attacked my computer) I suspect the unfortunate UEFI who ate something bad during the qubes update
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Good to hear! Honor the old ways 
Oh whoops I replied to the wrong thing because mail moment I think LOL