I gave Immich a fair try, but it could not replace Apple Photos for my use case. YMMV, but my favorite Photos app features simply weren't available.

I use Apple's top-notch editing for all sorts of stuff - RAW images, videos, basic enhancements, etc. When I tested, Immich didn't have very good, if any, editing features.

I also love Apple's search functions, and it Just Works™. I'm sure Immich has similar, but I know it would take a lot of processing to make it happen.

I also did not really care for Immich's UI, it felt overly basic and Material Design to me, but that is only personal preference.

Another gap is metadata. In Apple Photos I can tap the little "I" icon to see a lot of capture metadata, and in Immich I did not see an equivalent to how good Apple's one is.