Unity doesn't create .sln file, "add .unityproj's to .sln" is disabled

Unity doesn’t create .sln file and “add .unityproj’s to .sln” is disabled (grey out) on External Tools section

Imgur: The magic of the Internet is my screenshot and version

I’m using windows 10 and VS2019 Community Edition

I tried many things that read from this forum but didn’t solve.

It arose after upgrade to lastest Unity version.

I downgraded Unity then problem solved.