certifications are only "required" if you need something that requires it.
I.e. a basic OW certification is generally required to get air fills and entry into some parks/boats. It is not required if you have your own compressor and are going to dive in unregulated areas.
A nitrox card is generally required when you want to get nitrox, but if you have your own way to blend it then it's not required.
AOW to get to 100ft, etc etc.
The FFM course is not required by anyone to my knowledge outside of some institutional stuff. The aquariums I have dove in haven't required me to show proof of a certification but I have had to "pass a test" that the DSO has set up and I'm sure
@Hoyden has something similar at her aquarium. Our DSO at the university requires demonstration of skills prior to allowing use when students need them for scientific stuff. This is one of those courses that have some nuances to make the skills easier and some time with an instructor will help IMO. A card isn't required, but time with someone who actually knows what they're doing is good. Someone like Jackie who uses them every day is going to be far more in tune than someone like me who can dive them but only does it a handful of times a year and only because I need the comms for whatever jobs are being done.