I did not contact Apple Support about Retouch until November 11, 2024 - ten days after -Alex D.- began this incredibly helpful thread. I still think it is most telling that all of the Apple Support personnel with whom I interacted - and who interacted with each other in working to help me - literally had no clue Apple had removed Retouch. They were certain my being unable to access it was simply an issue specific to my computer and they could walk me through restoring ReTouch to my Photos. And they continued working to do that even after I told them I was pretty sure it was gone.
As noted, Apple Support assured me multiple times that ReTouch had not been removed. My main Support repo also had me hold several times while he consulted several of his Support co-workers - returning in between to assure me ReTouch wasn't gone. The last time I held while he and other Support co-workers researched the issue further, he returned and reported they had learned that ReTouch had indeed been eliminated. That is when I asked him to walk me through how to downgrade from Sequoia. He immediately knew that was now impossible, informing me once you upgrade to Sequoia you can never return to a previous operating system version.
The Apple Support staffer I spent a lengthy amount of time talking with - as well as his Support co-workers who also tried to help me - were super helpful and most genuine. They really wanted to help and were sincerely disappointed when they learned that they could not restore ReTouch to Photos for me. At the time, the fact Apple had not informed Apple Support personnel of the elimination of ReTouch -- and I had been the one to tell them - really surprised me. That was a first in my Apple Support experiences Later, after posting in the Support Community on this issue, it also raised red flags for me. Why all the secrecy, silence, etc. etc.?
And thanks for the idea to screenshot, document comments, NaturesPagan. I wasn't doing that to begin with, but I have been lately.