Hi! I hope it could be help.
First of all, I used .gitignore template below.
It excludes dll, cpp.obj, and more. It means that the core of plugin cannot be committed, pushed, and shared.
GitHub Desktop says “0 changed files” and I understood it that every file is committed, that was mistake.
So, I edited .gitignore temporally and commit exact every file in plugin, then no error detected.
That’s all what I did.
Addendum:
I placed Plugins folder to same hierarchy as (ProjectName).uproject file and Build, Config, Content, Intermediate, Saved folder.