You're amazing all praise to the devs, but for your stupid friend here, i create the keys on amber and after create the account on nsec app?
If you have a nsec.app account you can use that, just need to create the app first in amber and then you can login to a nostr app using your-user@nsec.app
If you have your own domain you can use that too
Example:
https://github.com/greenart7c3/greenart7c3.com/blob/main/.well-known%2Fnostr.json
Discussion
You create the account in nsec.app first if you don't have one yet.
When trying to login to a app go to amber first and in the permissions screen press the new app floating button. then you will be able to login