Can I manage the Recents Folder?

Only if you want to delete the files. A Smart Folder collects the files that match its criteria to display them in one place. They are not an alias or copy. They are the actual files.

If you don’t like the results, but would like some similar functionality, you could make your own Smart Folder with the criteria you choose.

All the contents can disappear if the Spotlight index is corrupt, or the specific metadata gets removed. I don’t know how they could get removed unless you restored all of them from a backup.

You can’t edit the Recents criteria, but you could create your own Smart Folder.

Create or change a Smart Folder on Mac - Apple Support

So why have almost all the files suddenly disappeared? I didn't delete anything. Where can I edit the criteria? Only a few pictures are currently showing and far from most. No documents, or anything else... It seems to me that the update of High Sierra (10-13.6) has changed the settings.

OAC-ChrisMathieso wrote:

So why have almost all the files suddenly disappeared? I didn't delete anything. Where can I edit the criteria? Only a few pictures are currently showing and far from most. No documents, or anything else... It seems to me that the update of High Sierra (10-13.6) has changed the settings.

The last update for High Sierra was a Security Update and was in November 2020. This posting is appearing in Big Sur. Can one please clarify.

Thanks, Barney. I guess the index must have corrupted itself, although recent updates might be involved. If I move from 'recents' (which has a total of 8 sundry files between 2013 and 2020) to 'This Mac', I get jpegs from 2006, which is quite good even for a 2011 iMac. But the record dies in 2018. Maybe the index caught Covid? It has never been that helpful, but since the Finder always starts there, one wonders.

Try resetting Spotlight

In the Terminal type

sudo mdutil -E /

type your password as requested (there is no feedback as you type)