In Germany and Austria it is required to use a bank account which is owned by the pre-company while creating a company (i.e. you cannot use your private account). The inital funding has to be sent to this account and is then approved by a district court.
Bunq requires you to have a commercial register number. In DE/AT this number is assigned after the founder contract and the confirmation of the initial deposit was sent to the district court, i.e. you have to have the bank account before you get the number.
Consequence: You cannot use bunq as main account for a new company in DE/AT (you can only switch once the company was founded, but you need another bank account first).
A good explanation (in German) how this procedure works and which steps must be taken can be found here: https://support.holvi.com/hc/de/articles/115005674825-Gr%C3%BCnderkonto-nur-f%C3%BCr-Deutschland-