Being underestimated is a head start disguised as an insult.

When people decide you are not a threat, they stop watching you closely. That inattention is room: room to practice badly, to try things, to get good without an audience keeping score. The sting is real, and it is also the price of the cover.

Notice where you are being written off, then use that room instead of arguing with it. Pick one thing you are quietly getting better at and keep it off the record for a month. Let the result be the first thing anyone hears about it.