I’ve installed the 2021.3.1f1 version of Unity and when I created a projects I got lots of errors regarding packages not having meta files. There’s also warnings about meta files not having a corresponding asset. I tried creating/opening projects but it didn’t help. I then tried to switch the Unity version but I still got the same errors. I’ve tried reinstalling fully reinstalling Unity but thet didn’t help and reinstalling the packages.
Extra unwanted packages in new projects (collab, testing, rider and other junk):
About the fastest way I have found to make a project and avoid all this noise is to create the project, then as soon as you see the files appear, FORCE-STOP (hard-kill) Unity (with the Activity Manager or Task Manager), then go hand-edit the Packages/manifest.json file as outlined in the above post, then reopen Unity.
Sometimes the package system gets borked from all this unnecessary churn and requires the package cache to be cleared: