I have not—any in particular to try?
The list of self-hosted photo/video sharing options I’ve found so far is below. Before trying each, I wanted to see if someone here might mention what they are already using that hits on the functionality I'm looking for without having to try them all:
Chevereto, Immich, LibrePhotos, Lychee, Mediagoblin, Nextcloud Photo Gallery, Photonix, PhotoPrism, Photoview, PiGallery2, Pixelfed, Piwigo, Synology Photos
I can try adding some DAMs to the list as well, to focus on pure file uploads and downloads and get away from the specific photo/video aspect. However, that might stray from this feature:
"Photos on iOS can be downloaded as photos easily, not just saved as files"
…which would be nice to have. Especially from some family members who would have no idea how to access photos they downloaded as files on iOS if they didn't show back up in their photo library.