nostr:npub1g0wmxtcsjnnmq7x2vdpymczss47ch5gzuwfkw47s22lehvklxa2scpuvzk From what I can tell, nope! Just based off of this. https://github.com/mastodon/mastodon/discussions/22315#discussioncomment-4405328
Discussion
I think they’re talking about ActivityPub keys there, but it looks like your Nostr private key is derived from your ActivityPub ID plus some secret in a configuration file. Every time you post a note to Nostr, Mostr regenerates your key to sign it. There’s no API to just return your private key.
https://gitlab.com/soapbox-pub/mostr/-/blob/develop/src/nostr/sign.ts
This file describing users’ profile metadata includes a field for “lud16,” which would be a Lightning Address. So maybe it’s possible to set that through a Mastodon client?
https://gitlab.com/soapbox-pub/mostr/-/blob/develop/src/nostr/schema.ts