All Nostr key holder apps should support multiple identities!
Nostr has some strengths:
1. you can reuse your identity across apps
2. you can create multiple identities (for different use cases)
Identity creation is easy, but switching between identities should be easy. as well Therefore all Nostr key holders -- signers (Amber), extensions, bunkers -- should be multi-identity. Unfortunately that's not the case for most extensions.