I have been thinking about onchain privacy in bitcoin and have an idea, which I cant tell if it is possible to realise:

Alice sends Bob some sats to a public key which can be verified with its balance and received transactions in a blockchain Explorer. So far, so good and exactly the same as now.

Bob receives the sats and he has now a new address which he can use for spending the sats, but a different address than the one he received it on.