So if you have multiple frontends that talk to the same API layer, then:
(frontend1, frontend2.. frontendN) API Layer SuperTokens core
If you have multiple API layers per frontend:
(frontend1 API layer1, frontend2 API layer 2.. frontendN API layer 3) SuperTokens core. This will share the same users across all frontends
Finally, you can run one core per frontend and backend. This will essentially create different users per app..