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. :)

Thanks for the reply, and for the forward. Sadly, it doesn't seem to work, USD is the sole option. Could it be because I'm on Firefox? I've read that some sites act up on Firefox.

When you are on the latest version, I would say no it isn't, because I am also using Firefox (PC/Windows 11) and I also ran into the same problem you are facing. Another member also had this problem and was able to solve it with the same trick.

Are you by any chance using an ad-blocker, 3rd-party script, proxy, VPN? Do you allow websites to access your physical location? Which location is displayed when you are visiting the Google main page, does it show a location close to you or a different region/country?

Lastly, you may wish to check the language and currency settings (see attached screenshot) and try the same trick again. If it still doesn't work and in case you are using uBlock or a similar ad-blocker, deactivate them, refresh the page, accept cookies if you haven't already, and it may work.

A few years back I could set any of the available currencies (US$, Euro, Russian Ruble, and a couple of others, I think, I don't remember), but now it's only US$? It's not just counterintuitive, it's very weird as well. :|
Ah, but thanks for the reply. I now wonder if it's the same for other non-EU countries that neighbour the EU?