Authelia is an authentification provider. So you can have a single login for all your services. It can provide autorisation and authentification with a single unified login.
Bitwarden is much "simpler", in it's just a passwordmanager. As soon as you start sharing passwords, like you do in bitwarden, you lose the authentification part, even worse, you lose control over the shared login. Anyone with autorisation can "steal" the login as in unauthorized copying/distributing the password or even changing the password alltogether.
With an sso like authelia you can mitigate such attack vectors.
I see a big problem in every approach, probably because I don't understand something
When i'm using just bitwarden, all my passwords for every service are different, but the ui is opened for anyone to see
When I use authelia without oidc I add complexity of using the services, and probably two passwords to type manually, or a locked down system(which is cool)
And if I use authelia with oidc, it means I have only one password for all of the services (manual, or in bitwarden (which has its own manual password))
I use authentik but believe it's similar. You can create accounts for people and give them passwords, or send a welcome email asking them to register to create one. I would warn you though, not every service has the ability to use it and it does take quite some effort to get it working! It's interesting to learn about though
If you are looking for user management and registration, then Authelia is the wrong software for you.
Authelia is a very light weight security layer (and more recently SSO) that is only meant for few users precisely because it doesn't have an onboarding process, dynamic access control, and more advanced features. Everything is done through config files and secrets. The admin has to manually create a file or plaintext lines with the user and password for each new user and restart the container.
Authentik is what you want if you want a bunch of users and new user sign up.
As for bitwarden/SSO, they should be fully separate. Otherwise you will likely break Bitwarden app and browser integration functionality.
You also do not want to run into the case where you don't know your SSO password so you can't get into bitwarden to find the password and you are screwed.
Bitwarden, TOTP method, and SSO should ideally be separate and you should be able to access your passwords and TOTP without requiring any password that is exclusively in the Bitwarden database.
Most things should be behind Authelia. It's hard to know how to help without knowing what exactly you're doing with it but generally speaking Authelia means you can have SSO+2FA for every app, even apps that don't provide it by default.
It also means that if you have users, you don't need them to store a bunch of passwords.
One big thing to keep in mind is that anything with its own login system may be more involved to get working behind Authelia, like Nextcloud.