Bug The assets have lost previews from 3d models and prefabs

After the transition of the project from URP to HDRP, previews disappeared in assets on 3d models and prefabs. After re-importing, only black previews appear

 

@M4nTiC0re back up your project before you try anything (and I hope you backed up before you did the change.)

I would try deleting some or all of the Library folder contents and see if that helps after Unity rebuilds it. I think the Artifacts folder might contain the intermediate versions of the assets etc. Unity uses. Anyway this has helped me many times when some assets have seemingly corrupted and I've verified the the files (PSD or some obj/fbx file) are otherwise ok, but Unity is unable to use them correctly.

 

I have a copy of the old project at the URP stage, but I decided to deal with the issue of displaying assets only now. Although a little time has passed, but I don't want to come back again. What exactly should I try to delete? Everything where there is no preview or delete assets by the type of HDRP and URP settings? Before installing HDRP, I deleted everything related to URP

 

Shut down the Unity instance you are running.
Then go to the Library folder under your project root, and then delete the Artifacts folder inside.
Now when you restart Unity, it should start to rebuild the missing stuff in the Library.

 

It didn't help me. It seems that I did everything exactly like this