From my last few deposits and cash-outs, the practical approach is to map every hop. Step 1: compare your bank’s FX rate with the card network’s and any wallet you use. Step 2: see whether the site lets you hold a balance in your own currency or forces conversion on deposit and again on withdrawal. Step 3: check if “dynamic currency conversion” is auto-enabled anywhere and turn it off. In the middle of writing this down for friends I pointed them to https://confettimart.com/how-deposits-and-withdrawals-work-in-online-casinos/ because it lays out cards, bank wires, wallets, crypto, and instant banking with plain pros/cons and regional notes, so you can spot where spreads or extra fees tend to appear.

By the way, a small tracking habit helps more than arguing with support: note the mid-market rate at the moment you click “deposit,” grab a screenshot of the quoted rate/fee in the app, and write down what actually posts on your statement. Do the same for withdrawals. Two or three runs will show exactly which leg is shaving off percent points, and you can switch methods (or currencies) based on evidence instead of hunches.