Immich all the way. It is very similar to Google photos in terms of UI and features and is being actively developed. You can create shared albums with unlimited contributors and also share an album by its link.
I have used Nextcloud before, but the feature set (even of the memories addon, which is supposed to be better than the default photos app) is severely lacking and Nextcloud is incredibly slow compared to immich.
Yes, I’ve been using them extensively. AFAIK you can’t change a private album to shared, but have to create it as a shared album from the beginning.