Majority of apps are B2C apps, they don't need any of this.
All you need is Apple and Google Oauth.
It depends on your use case.
If you are a B2C app, you are probably more concerned about:
- social providers (Apple and Google being the big ones, but others could play a role--FB or Tiktok for example)
- easy registration (but not too easy, you want to avoid bot spam)
- self-service account management (updating profile fields, consents [CCPA, GDPR, others], resetting passwords
- single sign-on between your apps (if you have multiple)
- language support (for your backend, and mobile/web front end)
- cost
- possibly MFA, possibly passkeys
If you are just starting out its probably a good idea. Think about the use case when google bans either your app or bans your app user?