There is no way to find an address that you sent funds to in the Monero wallet if you didnt save the address. This makes creating a proof with the transaction key on monero.com explorer useless.
There should be a field in the tx details within the app of the receiving address if it is a spend tx.
The default behavior in Cake/Monero.com is to save recipient addresses in transaction details, so either you’ve disabled this behavior in the privacy tab, or perhaps you’re encountering a bug.
Would you mind checking your settings at Privacy > Save recipient address and reporting back?
Ok. Awesome. I had it turned off. I think my reasoning a long time ago was that it would save it to contacts instead of implying saving to the tx details.