I updated to Sequoia 15.8 a few days ago and I am experiencing the bug discussed below. QuickLook for raw images (NEF, in my case) does not work. Relaunching the Finder briefly helps. Unmounting my camera cards after importing NEF images fails requiring a Force Eject.
Fortunately, Adobe Lightroom seems to work so I can still import and edit images.
I can wait for Apple to fix this or go the nuclear option and downgrade to 15.7.9. 
Edit to Add: Have filed a bug report with Apple.
This is a disaster for professional photographers (not me). So I am going to wait for a fix. I have seen a reddit post which says the beta of 15.8.1 fixes it, but not convinced yet. I will try this tomorrow. Has anyone else moved on to 15.8.1 beta? And, yes, I filed a bug report.
This is from a post on the thelightroomqueen.com forums:
I’ll wait.
Can you update to today’s release of macOS 15.8.1 and see if that fixes the problem?
I just installed macOS 15.8.1 – which also updated RosettaUpdateAuto.
QuickLook on raw images (NEF and ARW, in my case) work again so the update fixes that problem.
Also, XProtect was not updating and manually checking would fail. It still fails – so XProtect is not updating on Sequoia. Currently it is v5360 but should be 5362.
One problem fixed; one remains.