I use Synology Photos, has worked quite well, but that’s obviously only an option if you have Synology NAS.

I’m currently using Immich & Nextcloud too. I have some backups in Google Photos, but mainly trying to keep a hold of the photos myself. Having Immich & Nextcloud at least gives me two copies of my photos as a precaution.

Have you tried Syncthing? It’s not the same as Google Photos, but I think it’s one of the best file synchronization software yet. I don’t use it to sync my photos, though, I use it for syncing my markdown notes.

I use OneDrive for the auto-upload feature. I know it’s not selfhosted, but I want an off-site copy of my pictures anyway, and the phone app works really well for auto-uploading. I had previously tried Nextcloud’s auto-upload, but many times the uploading was stuck and I had to fix it manually.

I then have nightly rclone jobs to download the photos from OneDrive and store them locally. To view them locally, I use Photoview, which works really well with an existing directory structure.