PhotoPrism is easy to setup with NextCloud sync, though it seems a bit odd the way its done. The NextCloud server is added to Settings / Backup in PhotoPrism, then you can click the circular arrows under the sync heading, and setup sync. To pick up the NextCloud auto uploads from my phone, I selected the InstantUploads folder to sync, with a daily interval. I told PhotoPrism to download remote files, preserve filenames, and sync raw and video files. I didn’t want PhotoPrism to upload to NextCloud as I wanted it to be a one way file sync to gather data. My PhotoPrism server is setup as a data viewer and not generating data itself as well. Then a flip of the “enable” switch and its complete. The first sync didn’t start instantaneously, however it did start not too long after setting it up, and it took a few hours to slowly sync and process all the files in my NextCloud folder (a few thousand files).