There is a problem with cmd+h or ctrl+h on macOS. By default cmd+h is used for hiding current window. So trying to search globally on all tabs not working. If you try ctrl+h instead (cmd+f and ctrl+f are the same for example) editor switching tabs instead of global search.

PICO-8 ver: 0.1.12c

I accidentally figured this out... If you press ctrl-f to search, and type what you are looking for and THEN press ctrl-h (while there is text still in the search bar) then it will global search, not switch tabs.