I have spent a long time at Synology Photos, along with my family. We have tags and albums. Is there a good way to migrate? I'm even open to migrating manually (album by album) if I could trust the process.

You could use the migration tool and keep both until you are sure if it's worth changing.

https://github.com/simulot/immich-go

This looks like it for Google photos.

It imports from folders or google photos into immich. I used it to import my photos

You probably arent going to use synology photos long term anyway, unless you plan on buying synology products forever even when they go back and forth on anti conumer things (requiring synology harddrives).

I use immich on my synology NAS and i am happy with it. I did not migrate from synology photos though so I'm not sure how you'll be able to retain your tags and such. If it was me id set up immich going forward and then work on migrating old data

I originally tried immich on pikapods but at the time I was having trouble with family members being able to log in and view photos. I switched to Synology photos because it should just work and has for the last 2 years or so. I have regretted it for the sole reason that it entirely relies on Synology.

I don't have an answer for you, but I am very interested in any replies. Immich looks like it has matured a lot since I last used it (over 2 years ago).

I'm thinking maybe I can do a manual migration dragging from folder to folder. I'll report back.