Missing Package Manager Case (possible) Fix

I loaded an old project of mine in 2018.3.12f1, clicked on Play and got a bunch of errors related to a package that was installed in my project. Since this package was not used in my project, I decided to deinstall it but, oh horror! the package manager link in the Window menu was missing!!!

After a while wondering what I should do, I decided to investigate the packages that were present in my project. I right-clicked on the one that generated errors and clicked on "Show in Explorer".

I quit the editor and deleted all the packages that were in the window that opened (LoadedProject\Library\PackageCache). After starting the project again the deleted packages were reinstalled.

Doing that not only fixed the errors in play mode but the Package Manager was back in the Window menu!

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I hope this will be helpful if you have that specific problem.

 

I have a similar problem except that my project won't open back up (it stays on the splash screen forever) unless I delete my whole Library.
Deleting the PackageCache is not enough and somehow when I open my project back up after deleting my Library, all my references on to other gameobjects are lost. So it would be a nightmare if I had to re-reference every single of them.

 

If I remember correctly, this issue stems from the fact that the package manager is itself a package. So when Unity boots up and there's an error, all package code isn't compiled - this includes the package manager.

In other words, having an issue with a package means no package manager, which often means you can't update the package. This is a known issue, although I don't know if or when they're going to fix it.