How to design Architecture of Backend with multiple back and frontends

So I am building a Web-Application that is feed data from some external system. This Web-Application should then support different options for calculations / Graphics / different Layout / ... depending on who logs in (Users from different User groups working on different Data (But same kind of Data)). The differences are mainly in the backend.

Some of the functions such as Authorisation / Authentification / Cookies / receiving data are the same for all User groups.

Are there some Architectural guidelines about how to do such a thing? Or maybe some good book or YT-Series that I could consult? I read about white labeling but that does not reuses the recurring functionallity.

Other approaches I thought about are:

A) One Endpoint handling Authorisating / Cookies / ... and then sends the request to some internal sub Endpoint handling the group specific request. With multiple frontends.

B) One large Backend doing everything. With either one or multiple frontends.

C) Multiple disjunct back and fronends where everything is implemented starting from some whitelabeling skeleton.

D) Multiple backends that inherit common functionallity and extend for specific functions.

Thanks for any help.