I am migrating to Nextcloud memories and move away from Google photos however my previous phones and family are linked to the Google account is there a way to compare all the photos on my local gallery to my Google photos to make sure I have downloaded all the photos from there I don’t have time to download everything from Google photos and delete duplicates
Well, grab any file manager app (I use Root Explorer, or the free version thereof) and you could check the count of files in your photos folder (probably DCIM\Camera) and see if that number jives with the number of photos Google reckons you have in your gallery.
Root Explorer can only view local files and can’t hook up to Google’s cloud services at all. So by definition anything it’s showing is physically located somewhere on your phone.