Newer iPhone export Photos in heic format. Photoprism should support that format (see Photoprism Doc but is returning on importation the error
import: failed to create preview image for ####.heic (file type heic not supported)
On this issue I found an explanation here
https://github.com/photoprism/photoprism/discussions/4073#discussioncomment-8630228
which seems to say that in the current version there should be no file /usr/local/bin/heif-convert since this is a depreciated script causing that issue. But I can find this file in my syncloud docker installation under /snap/photoprism/current/photoprism/...
I don’t know if this is truly the reason for my issue - but if Photoprism is not on the current version could you do an update?