Ente is a tremendous proposal. I don't know why I hadn't heard of it before, but I don't think it meets what I'm looking for. But the fact that the software is completely open is impressive.
While I really like it — snappy and encrypted — I was surprised by how much the missing Ultra HDR implementation affects me. Photos are currently uploaded with brightness information but not displayed with it. Therefore, my photos look great in Google Photos but far less vivid in Ente.
For what it's worth, I found a discussion about Ultra HDR. It doesn't seem to be a priority right now, though: https://github.com/ente-io/ente/discussions/779