Plex camera upload from iPhone and iPad

I have an iPhone and iPad, whose photo/video libraries are linked with iCloud photos. I want to keep them linked for easy, built in access to my more recent photos, but I’m looking at using Plex as a backup for my photos, mostly older ones. Would setting up the camera upload from both devices upload duplicate photos or would the duplicates be filtered out?

As a slightly related question, if I reset my phone to factory settings (no restore from backup) and then set the Plex app back up again to upload my photos as before, will it duplicate the photos then?

Does anyone have any experience with the above scenarios, and can offer advice? Thanks.