Legal layman's answer from a real estate banker (law studies were a long time ago):
You have concluded a legally binding purchase contract, which is the basis for the earned broker's commission. The right of withdrawal is a dissolving condition, which according to your information does not change the fact that the broker has earned his commission (at least it seems there is no corresponding clause in the purchase contract).
It would have been different if the bank's financing commitment had been a suspensive condition. In other words, the purchase contract would be pending until you obtained the financing. Then the broker would not yet have had a claim to commission.
Yes, great, that sounds conclusive. The purchase contract is concluded, the broker earns his commission. I can still withdraw, but that does not change the fact that the contract was concluded and the broker has a claim. Thank you very much.
I have read the 2015 ruling on an almost identical case, but there the broker rejected the financing contingency only later. That was the difference here...