Last couple of days, I've experienced this same "Missing Remote Media" error message when dragging photos from FCP's browser or directly from Photos app.
There are similar complaints scattered on this user board, no proposed solutions worked for me.
Take a look at this Apple support article dated June 16, 2023:
If edits don't appear in photos imported into Final Cut Pro for Mac - Apple Support
They're cautioning that pictures with edits should not be dragged from Photos or the Photos Browser.
You must first export from Photos to a file folder, then import from that folder into FCP.
Sure enough, all of my pictures that had failed with "Missing Remote Media" had been previously edited in Photos.
So I dragged a few unedited photos; they import perfectly and behave properlyon the timeline.
This is a poorly conceived implementation of drag 'n drop.
It adds a layer of wasted time and duplicated file storage.
Organized folders within Photos App are now of no benefit to Final Cut editors.
Has something changed? I don't recall having this problem in earlier releases of Final Cut Pro.
Hope this post is helpful; I've already submitted a report to Apple