Why are you syncing from your phone instead of your Synology then? Can't you sync from your NAS then just have pictures uploaded as you take them? iOS has a lot of restrictions compared to Android so two days really doesn't feel like a meaningful difference from a week.

I’m not an Immich or Synology user but essentially the mobile apps end up replicating your whole structure a little better, at least when I did the iCloud library to Ente import.

I could have done a data download from Apple but essentially leaving the Ente app open and choosing my albums to back up was a “set it and forget it” process.