I live in Moldova, and for whatever reason GOG decided that US$ is the only currency available to me, never mind that Moldova is in Europe, a candidate state to join the EU, and will change it's default exchange currency from US$ to Euros starting with January 2025. So why isn't my region "eligible" to use the Euro? It's not like it makes that much difference anyway, since it's all paid for remotely.

Try the following: At the bottom of the store page, switch the language to German and back to English- or any other language you have previously set, and Euro should become available to you as your currency of choice.

If this fails you would have to file a support ticket. I forwarded it, so you might receive help soon, if this trick doesn't work in your case. :)