Accidentally Sent BTC to bitcoin core watch-only wallet with private keys disabled
The Bitcoin would then be whatever addresses your watch only wallet is watching. Bitcoin Core won't just generate a keypair and throw away the private key, that would result in fund loss. In a wallet with private keys disabled, it will only use what has been imported into it in order to create addresses. If nothing has been imported into it, then it won't be able to make new addresses at all.
If the watch only wallet was created by Specter and it imported keys into that wallet, then you should expect to see your Bitcoin in Specter as well.