To protect that precious thing you gotta go Igloo and Frost, and stick with Jumble or other clients that support Frost for your news updates. That is the only way right now you can avoid pasting your nsec anywhere online (and still generate new sign-ins).

Basically your nsec will stay offline, you'll generate Frost shards with it while offline, and then you'll paste those shards to online. From the shards there's no backwards extrapolating your nsec. Zero online exposure for your nsec.