On ADS-B Exchange they even have a filter option for military aircraft, and it will show all kinds of transport, mid-air refuelers, helicopters, and even training aircraft like the Texan, but I don't think I ever see fighter jets on there. Even when I see some F/A-18s fly overhead IRL I still never see them show up on any websites. Or like right now I noticed that Air Force 1 was flying out of Palm Beach I think it was but I didn't see any fighter escorts show up. Are fighters allowed to just turn off their transponders in civilian airspace?
Because they don't want to be seen.
Are fighters allowed to just turn off their transponders in civilian airspace?
FR24 and ADS-B Ex are not based on normal transponders (that would require access to actual RADAR data) but rather ADS-B and mode-S transponders. The military can simply choose not to operate with this equipment. This does not make the fighters invisible on normal ATC radars, since ATC obviously still needs to be able to see them.