git. How to maintain multiple projects with one core?

Question

git

Hello!
The bottom line is this: now there is one project on Bitrix that needs to be cloned into new 2-3 projects, and then everyone will go their own way. But the current project will remain a certain core of all new ones. Each project will develop in its own way, in accordance with the tasks set, but their "core" remains the same. It seems to be acquiring additional functionality.
At the same time, it is known that the "core" itself will still be improved (bug fixes, innovations, etc.) and these improvements must be transferred to all other projects.
Hence the question: how to properly organize this process? Should new projects be moved to a separate branch of an existing repo or can they be moved to separate repos? What to see, what to know?
Thank you!

Answer 1

Make the shared project as a submodule for the rest