Immich is one of the only apps on iOS that properly does background sync. There is also PhotoSync which is notable for working properly with background sync. I'll take a wild guess that Ente may have got this working right too (at least I'd hope). This works around the limitation that iOS apps can't really run as background apps (appears to me that the app can wake up on some interval, run/sync for a little and try again on the next interval). This is much more usable then for example, the Synology apps for photo sync, which is, the last time I tried, for some reason insanely slow and the phone needs to have the app open and screen on for it fully sync.
Some issues I ran into is the Immich iOS app updating and then being incompatible with the older version of the server installed on my machine. You'd have to disable app updates for all apps, as iOS doesn't support disabling updates for individual apps.
In my specific scenario, the latest version of Immich for NixOS didn't perform a certain migration for my older version of Immich. I had to track down the specific commit that contained the version of Immich which had the migration, apply that, then I was able to get back to the latest version. Luckily, even though I probably applied a few versions before getting the right one, it didn't corrupt the Immich install.
The reason is that I want to keep the services in a portable/distro-agnostic format and decoupled from the base system, so I'm not tied too much to a single distro and can manage them separately.
My understanding is that when using containers updating is an ordeal and you avoid the need my never exposing the services to the internet.
Containers decouple programs from their state. The state/data live outside the container so the container itself is disposable and can be discarded and rebuild cheaply. Of course there need to be some provisions for when the state (ie schema) needs to be updated by the containerized software. But that is the same as for non-containerized services.
I'm a bit surprised this has to be explained in 2025, what field do you work in?