Desktop and Finder won't show preview in icons

Simple check use guest user / another user (if need create one) and see you get icon preview?

(Make sure you copy some of the sample files to shared and check)

Please check in Safe Mode if you have the same issue?

https://support.apple.com/en-us/HT201262

Note: Safe mode prevents your Mac from loading certain software as it starts up, including login items, system extensions not required by macOS, and fonts not installed by macOS. It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. And it deletes some system caches, including font caches and the kernel cache, which are automatically created again as needed.

I'm having the same problem but with raw files from a Sony A7rM4 camera (The camera is listed as supported on https://support.apple.com/en-us/HT210191 as a "Sony Alpha ILCE-7R IV").

• When you search on this "community" for this type of problem there are entries going back to at least 2011 with different file types and with raw files from different camera types; why hasn't Apple support gotten involved and solved this issue?
• Each entry seems to have the same unhelpful entries such as provided by Sharhari and Eau Rouge in this entry; and then after a few simplistic questions they all go silent and the problem is never solved. It makes me think that they just paste in some answers so they can up their points count but don't really know how to address the problem.
• I have tried all those suggestions many times without any success.
• If you try to open a support ticket with Apple at https://getsupport.apple.com the only option is a phone call ... why don't they have a support structure like this communities page?

Could be a corrupt preference file.

Click once on the Desktop.

Click Go in the menubar.

Select Go To Folder, enter the following text,

~/Library/Preferences

press Go.

A new Finder window with the folder highlighted.

Scroll through the folder till you find com.apple.finder.plist

move this to the Trash.

Restart your mac, a new com.apple.finder.plist will be generated.

When your mac starts up click on View in the menubar and select

Show View Options and make sure Show icon preview is selected.

Does this make a difference.

Resetting the NVRAM worked for me: https://support.apple.com/en-us/HT204063

Did you encounter any error / issues while restoring from Time Machine backup?