Yes CCF2/KN95/N95 masks are still required on all public transport in Southern Germany (although other parts of the EU dropped this in May) - buses, trains, trams etc.
That free bus service (or at least it used to be free) from the ferry terminal/Zeppelin museum to HAM RADIO 2022 at the Messe, runs on a regular basis. As you will see, one route goes via the train station as well.
The current weather forecast is for 13 to 14 hours of sunshine and temps in the high 20’s all three days however heavy rain showers are expected on Friday and lighter on Saturday, so some lightweight waterproof jacket is advisable to get from the car/camper parks to the buildings. Everything including the flea market is inside of course.
PS Just an FYI - this is the current entry to Germany regulations around COVID (since June 11th no restrictions apply except for people coming from China):