OK, apologies, I should have been properly specific in my original post.
I wish to identify caches, from a specific area, that I have not found, that I do not own, that have not been found in the last year.
Looking again at your link and comments I have come up with this procedure:-
Statistics => Days Since Last Found
Profile name: Select yourself.
Cache location: Select the area you are interested in.
Add filter "Hide Found / Owned / Not found".
Check 'Found' & 'Owned' (which is counter intuitive).
Click Filter.
Locate the page where 'days since last found' drops below 365.
Note the number of the line with the smallest 'days since last found' greater than 365.
(I.e. the # number to the left of the blue line) Call it 'X'.
Scroll up and click on "Create a map".
Set "Number of caches" to X.
Click "Create Map".
This seems to work, though it's a bit cumbersome.
I also tried "Add to Virtual GPS" and successfully created a new list and then exported it as a GPX file, not that I think I would actually use this.
It would be nice if there was a simpler tool but the above works well enough.
The challenge checker you mention I already link to (
https://coord.info/GC2HD75).
Thanks for your help!