I'll throw in another "+1, quite satisfied with immich" comment, because I'm honestly that impressed.

The project as a whole feels competent.

Stuff that should be fast is fast. E.g. upload a few tens of thousands of photos (saturates my wifi just fine), wait for indexing and thumbnailing to finish, and then jump a few years in the scroll bar - odds are very good that it'll have the thumbnails fully rendered in like a quarter of a second, and fuzzy ones practically instantly. It's transparently fast.

And the image folder structure is very nearly your full data, with metadata files along side the images, so 99% backups and "immich is gone, now what" failure modes are quite easy. And if you change the organization, it'll restructure the whole folder for you to match the new setup, quietly and correctly.

Image content searching is not perfect (is it ever?), but I can turn it on in a couple clicks, search for the breed of my dog, and get hundreds of correct matches before the first mistake. That's more than good enough to be useful, and dramatically better than anything self-hosted that I've tried before, and didn't take an hour of reading to enable.

It's "this is like actually decent" levels that I haven't seen much in self-hosted stuff. Usually it's kinda janky but still technically functional in some core areas, or abysmally slow and weird like nextcloud, but nope. Just solid all around. Highly recommended.

How does the mobile syncing work?

Really looking for a system where I can install the app on my parents' iPhones and it backs up their photos to my server without them having to even know about the app. They won't open it, ever.

Nextcloud fails at that.

This 100x.