Thierry-Indigo-Zebra Individual transactions are not communicated with any tax authority by default. Only your balances at the end of the year are communicated.
Any European tax authority has to do a special request when they want insight in your individual transactions as part of an investigation. These requests will be met by bunq, as they are obliged to comply with such requests.
As far as I know, bunq does exchange balances with the Dutch tax authority and the Dutch tax authority (Belastingsienst) exchanges information with the French tax authority as part of a EU-wide tax treaty.