Hi, you can turn off the password manager on the Settings page. See: Password Manager - Remember, delete and edit logins and passwords in Firefox - "Disable the Firefox password management feature" section.

Expanding upon the earlier reply, Passkeys are a little tricky. They're not stored in Firefox. They are stored on the device you created them on. A lot of sites/apps push Passkeys hard as the preferred method of authentication. However, although they are more secure in many ways, it's easy to get into a hole with them. Not all devices play well with others (I'm currently trying to figure out how to use a passkey I created for my wife on my Windows laptop under Firefox on her Windows laptop using Firefox).