Serbia ATM fees: According to most forums, all banks in Serbia charge between 450 and 600 RSD per withdrawal. But I found that the Halkbank ATM did not charge a fee for withdrawals.
Halkbank ATM in Belgrade, Serbia:

Halkbank is a Serbian bank, founded in 1990, previously known as Čačanska Banka.

And I can confirm that as of July 9 2024, using a UK-issued Monzo Mastercard debit card, the Halkbank doesn’t charge any withdrawal fee.
And as always, I like to show the proof. Here’s a screen grab from my bank app. I withdrew 7,000 RSD. No fee added:
