Since GNMath is static HTML/CSS/JS, you can clone the repository at home (over your unrestricted network) and run it entirely offline. On a school computer, open the downloaded index.html file directly from a USB drive. No internet connection required, hence no filter to bypass.
Because many schools block specific game sites, users host these games themselves on free platforms like GitHub, which might not be on the school's blacklist, allowing them to remain "unblocked" [1]. gnmath github io unblocked
Recommendation
: Over 100+ titles including rare web ports. Since GNMath is static HTML/CSS/JS, you can clone