In couldn't even remember my own until I recently switched to using my own domain so I could do nip46 login via Amber.
How is NIP05 related to nip46?
when logging into a new client you enter your nip05 and then get a prompt from your signer. behind the scenes there is a nip46 section in .well-known/nostr.json which lists nip36 relays for each pubkey.
So I need to change my nostr.json to support that?
yes, so the client know which relay(s) to use communicate with the signer. relay.nsec.app is a popular one even if you don't use nsec.app as the signer. you don't have to use the same address as you list in your kind-0 but it makes sense to.