When I go to d2_coast_07 my game automatically turns on mat_fullbright 1 but I can't turn it off without cheats. If it's forbidden to play like that, what should I do? My build is 4104 with ghosting mod.

Turn on HDR. Should fix it :)

EDIT: Set it to Full

it is allowed. that happens if you disable hdr in settings. you can turn fullbright off by mat_fullbright 0 (it is allowed as well)

@SKELETON You can also turn it off by typing the sv_cheats 0 command again or pressing the bind with the same command(on the next map after mat_fullbright 1 was enabled).