Thank you for the advice.
BUT, the next problem is:
fatal: destination path 'checkmk-telegram-plus' already exists and is not an empty directory.
I presume that this is the final problem.
If I (maybe) modify the library (although I do not know (yet) how) to make “checkmk-telegram-plus2” directory and than choose this one in notification settings…
OR maybe the developer (you?) to install the question “destination directory exists - rename?” 