Nostr login is the best method. As backup use a LN-auth from a dedicated LN wallet but not a custodial! If the custodial is closing your access you lose login to SN.

Why people rely so much on these custodial when it cost you nothing to create a nostr account or run a proper LN wallet?

Custodial accounts must be used only temporary, as decoy, as testing or specific one-time use. Not for long time and be dependale. Custodial = disposable