

Both Tuta and Proton have iOS apps of their own.
I don’t believe either can be used inside the native iPhone Mail app, since they use encryption schemes, which aren’t standard in any commonly used spec for mail apps, so no regularly available mail app can act as a frontend for Proton/Tuta, because no regularly available mail app “speaks” their encryption. (though on PC, Proton does have a Bridge application that can essentially perform the job of a translator in that case, but again, only for PC clients)
Maybe try Ente then?
Haven’t used it before myself, but I’ve heard good things, and it does have a memories feature, and it seems at least based on the examples on their website that it might generate something more than just “today x years ago”.
Unsure to what degree it works though, and unfortunately Ente is also a paid service (though it is privacy focused, and I believe it has a FOSS app too)
Seems like “Smart Memories” are on the roadmap for Immich though, so you might just have to wait a bit and can then switch once they’re there:
There aren’t really any other mature options out there for self hosted, or even just private Google Photos alternatives in my experience, so you’re kinda just stuck with Immich for the most feature-complete replacement, and Ente for a more “just works” private but not self-hosted one. Everything else is basically just a glorified file browser, but maybe with some smart searching or better media codec support.