There are no passwords to reset. You sign in with Continue with Apple, Continue with Google or Continue with Microsoft, or with Sign In with Company SSO when your organisation has set up its own sign-in. Most sign-in problems come down to which address the provider hands over.
Your discussions are missing
The address the provider gives us is the account. Signing in with Google one day and Microsoft the next, under two different addresses, makes two accounts, each with its own discussions and plan. Sign out and sign in again with the provider whose address holds your work. With Apple, choosing to hide your email gives a different address from the one you use elsewhere.
A team invitation does not appear
An invitation belongs to the address it was sent to. Sign in with that address and the invitation is waiting in Settings → Team.
Your company requires its own sign-in
If your team requires company sign-in, use Sign In with Company SSO and give your work address. Before an admin action the app may ask you to sign in again to confirm it is you; that is the team's setting, not a fault.
The Mac
The Mac works without an account. To connect it, open Settings → Account and press Sign In…: the browser opens, you sign in there, and the Mac receives its own token. If the browser finishes but the Mac does not change, press Sign In again.
Signed out unexpectedly
Log Out of All Devices, or ending one session under Active Sessions, signs those devices out at once. Sign in again; nothing stored on a Mac is deleted by signing out.