This is an issue with yt-dlp. It's unable to archive posts that are made up of multiple images. I cannot provide any 'open' examples of this here (a link was shared privately with me on Discord), but the format of the URL is:
https://www.facebook.com/permalink.php?story_fbid=XXXXXXX&id=YYYYYYYY
Here's the error yt-dlp gives:
yt_dlp.utils.ExtractorError: [facebook] XXXXXXXXXXXXX: No video formats found!; please report this issue on https://github.com/yt-dlp/yt-dlp/issues?q= , filling out the appropriate issue template. Confirm you are on the latest version using yt-dlp -U
This issue might be relevant: yt-dlp/yt-dlp#10058
The current 'solution' is to open each video individually and archive them separately.