Switched an appVM from Fedora 41 to 40 and Firefox is a lot better but still slow, which is strange. I see no recent Qubes updates.
Tried a new Fedora 41 appVM and still feels slow.
What could be the reason?
I see processes running using a lot of CPU: firefox, WebExte, kswapd0, Isolate+
It’s unusable at this state
Verify this:
Check how much memory is allocated to the Qube – there has been some issues with SE Linux and dynamically allocating the needed memory (if I understood it correctly) … so the qube would be stuck at the amount set as Initial memory.
The simple workaround, is to increase the initial memory in Qubes Manager → Select Qube → Settings → Advanced → Initial memory
Edit:
Read the link that @ludovic found - that’s what I was trying to write. 
Says it’s fixed 10d ago?
Thank you, this worked, but my concern is with having to run many appVMs with high RAM allocation which will limit the number of the appVMs I could run.
This is potentially a serious bug as could lock users out of their machines.
… but does you problem show the same “memory stuck at initial amount”??
Edit: After fetching more coffee, I see the “this worked”:
If you read the thread @ludovic linked to, I think there are some steps to restore the dynamic allocation of memory (change some SE Linux settings or reinstalling some packages). After those, you should have dynamical allocation of memory and can reset the initial amount to a low number again.