at minimum relays and clients will have the ips, browser signatures (in case of web clients). so two different npubs will be accessing same things from the same ip if you're using them concurrently.

ideally separate identities to different devices (best practice). at minimum use different clients and vpns/tor to access nostr with them.

also depends on your threat profile. but biggest threat to opsec long term is human laziness, so build systems with that in place - if you have a separate phone for just that thing then its way harder to slip up than if you need to remember to switch vpn/turn on tor, disable the other client etc. and then follow all of that for the rest of the time