Regarding Visual Studio 2022 I have had repositories/projects:
a) C:\_GIT\RepositoryA\Project1
b) C:\_GIT\RepositoryMain
Ok i found solution (needed stackoverflow and work colleague as rubber duck)
My copied C:\_GIT\RepositoryMain\Project01\Project01.sln
included 3 projects and one of them has relative path like:
Project("{FA807EC9-801F-11D4-BF68-00CB4F79EOBC}") = "Project01.Tests",
"..\..\..\..\Project.Tests\Project.Tests.csproj",
Which leaded to a) repository. I have removed all '..', now sln opens as single repository\branch