On Android we support NIP-55 remote signers like Amber - https://github.com/nostr-protocol/nips/blob/master/55.md

On iOS there isn't really a good NIP-46 remote signer available. I know nostr:npub1xtscya34g58tk0z605fvr788k263gsu6cy9x0mhnm87echrgufzsevkk5s is thinking of adding this to nostr:npub18m76awca3y37hkvuneavuw6pjj4525fw90necxmadrvjg0sdy6qsngq955 which would be amazing and we would support it straight away.

Not sure if nostr:npub1getal6ykt05fsz5nqu4uld09nfj3y3qxmv8crys4aeut53unfvlqr80nfm has plans for a mobile NIP-46 signer.