L To offer payment via iDEAL afaik it‘s required to show the IBAN to the user. So they could maybe hide it a bit more but someone who really wants to get this information would definitely still be able to get it.
With bunq IBANs there‘s also not really any way to misuse them. Direct debits are not automatically accepted like at other banks, and the IBAN isn‘t used anywhere to authenticate.
Of course, if you‘re worrying about this I would just recommend to either not use a bunq.me page at all or choose a sufficiently complex URL and maybe don‘t put your full name as display name.