Note though that you're going in September. Red Sea is very seasonal; every year is a slightly different -- "seasons" lasts longer / start later... But normally September is too late for hammerheads and too early for OWT. With some unluck it is a very bad month for shark sightings. Hammerheads June-July and OWT October to December. I don't have any personal experience from the Maldives in September, which is regarded as off/low season. December to April is high season with calmer weather, bluer skies and clearer water. With that said you can most certainly have great diving and see mantas, reef sharks and perhaps whale sharks there in September. Re coral, the Egyptian Red Sea has been one of the best, spared from bleaching due to its Northern location and relative cool waters. That changed in summer of 2024 when some of the reefs in Southern Egypt apparently were affected. Have not been after, so can't give a personal account of the severeness and if coral recovered or died. Maldives corals have been in a so-so state since 1998 when El Niño hit them hard and big parts of reef coral died. Parts have recovered and then been hit again by smaller bleaching episodes. Haven't been since 2018 (going in March 2026) so only info I've gathered, but then we could find healthy thriving reefs near channels that were swept regularly with colder deep sea water. Fish life great. Would recommend a central atoll live aboard as a first timer.
Good luck