I love immich, too, but I have also ran into a lot of issues with syncing large libraries. The iPhone app will just hang sometimes.
Like if I backup photos from iOS, then remove a subset of those from iOS to make space on the phone (but obviously I want to keep them on the cloud), and later the mobile app gets out of sync, I don't want to end up in a situation where some photos are on iOS, some on the cloud, but none of the devices has everything, and I have no easy way to resync them.
I have had the server itself fail in strange ways where I had to restart it. I had to do a full fresh install once when it got hopelessly confused and I was getting database errors saying records either existed when they shouldn't or didn't exist when they should.
I think I am a pretty skilled sysadmin for these types of things, having both designed and administered very large distributed systems for two decades now, but maybe I am doing things wrong, but I think there are just some gotchas still with the project.
iCloud / Google Photos just don't have that, they really never lose a photo. It's very difficult for me to convince my family to move to something that may lose their data, when iCloud / Google Photos works and is really not that expensive.
client_max_body_size 50000M;
proxy_read_timeout 600s;
proxy_send_timeout 600s;
send_timeout 600s;
FWIW, my library is about 22000 items large. Hope this helps someone.