Update: After several failed attempts of reverting back to 20.04 (which all showed that resume from suspend with nvidia-470 driver got stuck, although it did work previously), I finally decided to do a fresh install of Ubuntu 22.04 (using the existing partitions with no formatting, so my /home and other data remained intact).
And voila: now resume from suspend works without problems (using driver 515.65.01)
So maybe this issue is somehow related to the upgrade process?
Update: After several failed attempts of reverting back to 20.04 (which all showed that resume from suspend with nvidia-470 driver got stuck, although it did work previously), I finally decided to do a fresh install of Ubuntu 22.04 (using the existing partitions with no formatting, so my /home and other data remained intact).
And voila: now resume from suspend works without problems (using driver 515.65.01)
So maybe this issue is somehow related to the upgrade process?