How to properly maintain a base theme repository for future projects?

Question

CMS

There are:
1) a CMS theme developed from scratch. Stored in the git, all new projects start with it;
2) development team;
3) supported projects and new projects;
4) new features and bug fixes that are regularly added to the base theme.

I would like to know how to more correctly maintain a repository of such a basic theme and take into account all updates in such a way that developers can pull these updates into their projects with a minimum amount of effort (this is especially true for features, since not all of them are needed in old projects, so pull up stupid master is not an option).

It is clear that in this case it is necessary to create a separate branch for each feature and bug fix, but how correct is this in terms of labor costs and are there any better ways?

Answer 1

It is not entirely clear what is wrong with you, and where does the repository come from, since compatibility, features and branches are from different planes.
But maybe you are interested in Semantic Versioning