Before rushing to assess the impact of local events, the exit condition must be clear.
If the trip is imperative, such as for an urgent medical intervention or unavoidable professional obligations, the existence of a festival is just a minor distraction.
The risk here is overestimating a factor that, for many trips, is secondary and has no influence on the final decision.
You don't postpone surgery because of the Lille flea market; it's a false priority that can unnecessarily complicate already complex planning.
First, define the irrevocable objective before worrying about the atmosphere.