Man pages matching name rt::extension::jsgantt in section 3pm:

RT::Extension::JSGantt.3pm.en	debian 10 / rt4-extension-jsgantt
RT::Extension::JSGantt.3pm.en	debian 11 / rt4-extension-jsgantt
RT::Extension::JSGantt.3pm.en	debian 12 / rt4-extension-jsgantt