I don't think the Notre Dame fire was part of the plan, or allowed to happen by Q. Too monstrous a destruction of cultural heritage.
The overall white hat strategy seems designed to prevent civil unrest or destruction. Allowing the Notre Dame fire would not feel consistent with the wider picture we're seeing in how the Great Awakening and rollout thereof is being managed.
But given the scale of the war, we can't expect the white hat forces to be perfect and stop 100% of the cabal's destruction. So I think it most likely that this one slipped past.
(And I would not fault Q if that is the case.
Consider the cabal's goal involved nuclear war and massive depopulation, things like this are horrible but nowhere near the magnitude of what the cabal had planned. Q seems to be stopping an immense amount of evil.)
I had a similar reaction to Parkland. Cabal action, evil thing was not stopped in that case … but this is war. With all that is implied.