There is no clear cut answer to this question as there is no limitation .
FMA is showing its highest performance level which is CAT3 DUAL , it does not mean you can go down to cat 3 minima . Are you limited by crew qualification? Airport not authorising simulated cat 3? With AP ON , Passing DH , you are more doing a simulated CAT 3 approach than CAT 1. Or if you plan to disconnect by 80 feet you are then doing a simulated CAT 2 as Autopilot is not mandatory for a CAT 1 , and manual landing is required.
Now let's ask another question , simulated CAT 2/3 are not allowed in a busy airport in cavok weather.
Having CAT 3 DUAL on FMA , what is the lowest height at which you can disconnect AP?
I would say DH CAT 1 . Although your autoflight can do better , you are here limited by local airport requirements.