This depends, (sorry) if you withdraw USD from Etoro then yep Monzo will handle the conversion for you. If you withdraw GBP then Etoro will handle the conversion.
Another thing to think about is if it’s a bank transfer or card refund. If it’s a bank transfer, Monzo isn’t officially part of an international banking scheme so it might take a while to arrive and we do t handle the currency conversion as it’s handled by the banks that your payment first hits in the UK. If it’s a card refund, then USD refunds will go through like normal