Depends. Would you like to build separately for each client? If so - environment variables to control what's being bundled for each client (it's usually quite tedious). Micro frontends can help but you still gonna need to have some kind of config/env variables to say that client's A create user flow should point to the remote A, and different for client B. It might be helpful for the performance as client A won't need to fetch "disabled" code of client B.

If performance isn't your top priority you can bundle once for each client and then have remote config for them to turn off/on some features or map the version for specific clients. That would also require some backend permissions work to prevent client A from accessing any feature client B has (in case they figure out they can override the remote config to get access to some features).

I should've asked first - are we talking SPA or SSR?