There already is a checkbox there, under
'General - Non ISU'.
FWIW (to all here), these checkboxes shown in
@ABECyguy 's image are what I use to see only the forum categories I want and ignore all else.
Enable any combination of subcategories using those checkboxes there, then add a bookmark while you're looking at the currently filtered view - those view filters append unique parameters to the URL which can then be saved as a browser bookmark, or saved as one of the default pages to open with your browser every time.