I can confirm that bunq DOES NOT automatically release deposits after 30days in practice. Multiple cases for me both this year and last year, with different merchants.
Moreover, last time even a deposit explicitly refunded by the merchant was shown as denied payment and not released by bunq.
Last year I could request a refund from the app, but now bunq would not release anything without a WRITTEN PROOF from the merchant. Tried to contact support and they also do nothing without a written proof.
So my advice to anyone landing on this page is to never ever use bunq card for security deposits as it will either end up in a headache of gathering proofs or bunq will just steal your money.