Ok so the 'nsecbunker' is one of the first nip46 implementations, and it had it's own 'connection string' format - it was 'npub' or 'npub#token'. But now the new standardized format is bunker://pubkey?relay[&secret] - all modern clients will support this format, some old clients support the old nsecbunker format. Nsec.app can't work with npub or npub#token format bcs this string doesn't allow to pass the relay address, which is needed to run the nip46 protocol (original nsecbunker had hardcoded relays so that wasn't needed).

Thanks, I will adjust the wording. Basically, there are 2 kinds of bunker urls - with a &secret or without one, one with a secret must not be shared publicly, only pasted to the connecting app, nsec.app generates only urls with a secret now.