Signing apps! Something like nostr Connect, NOS-2X or NOS-2X Fox for web extensions. Alby had one. Android has amber I'm sorry I don't remember what the iOS app is, but there is one out there.

They can spin up new keys for you and manage multiple accounts. Or at least I know Amber for sure can, and NOS 2X Fox will im not sure if the iOS app does, but I don't see why it wouldn't....But these apps hold your private key for you kind of like a password manager and also like a password manager, They authenticate your actions on nostr.