The library actually is not very compatible with older Angular versions, I think this can be improved somehow.

If there are some code changes to improve this, these are necessary. If it's not possible because of Angular breaking changes between major versions, multiple libraries need to be released and maintained (following Angular LTS rules, minimum).

The first idea that came to my mind is to create a package for every major version, but this can be too much work. This will result in multiple demo apps too.