How to resolve below error ?

The .meta file Packages/com.unity.collab-proxy/Editor/PlasticSCM/UI/UnityMenuItem.cs.meta does not have a valid GUID and its corresponding Asset file will be ignored. If this file is not malformed, please add a GUID, or delete the .meta file and it will be recreated correctly

have you tried to follow the suggestion in the error? If states that you either should add a GUID or remove the files.

Just make a backup of the meta files and remove them from their current location to somewhere outside of your unity project.

Then reload your project.