Search within specified folder gives results but within 'This Mac' gives none I type Cmd-F and call up a search window; my search parameters are 'Name contains "xyz"'. Currently the search is limited to the current folder (~/library/preferences) and gives two results. Thinking to widen the search to see what extra files/folders might contain the term 'xyz' in their name I click the button to change the search from 'Preferences' to 'This Mac'. Now the search gives zero results.

Should not the search on 'This Mac' be wider than the folder-specific one? Surely it should, at the very least, return the two results from 'Preferences'?

Can anyone advise on this please?

Extra context: This is on a laptop that is connected to the Internet by wifi, but has no other external devices connected)
By default, Search 'This Mac' excludes System Folders

By starting your search inside ~/Library/ you are forcing it to bypass that default, as you are already inside a normally-excluded location.

To persuade it to add System Folders to a 'This Mac' search, you must specify as an additional parameter.
Click the + sign, top right [which then turns into a - ]
Add 'System files' &amp; 'are included' to your search parameters.