Open a support ticket. Just tried it now in Firefox and it works fine for me. If you have a similar setup (add-ons, settings) in both browsers, it could still be a problem on your end.

1. In Firefox, enter about:profiles into the address bar.
2. Create a new profile, which will get set as the default. That's not what you want, so set your old profile as default right away.
3. Launch the new profile in a new window. Open the add-ons manager there and make sure none of your add-ons are there. They can stick around when installed via Linux package manager rather than in-browser. Once you've double-checked the new profile is pristine, check if the refund forms works there.
4. If the problem persists, try enabling DNS over HTTPS / Cloudflare in the Firefox settings page, about:preferences then reload the tab with GOG loaded in it.

Edit: It doesn't look like you use GOG Galaxy, but for the sake of completion, I have to mention it can be used to ask for a refund as well. In the Deals category, there's the Orders History entry; from there you click the Ask for Refund link under an eligible order, as usual.

Also in another Thread someone mentioned that the "uMatrix" firewall can prevent certain GOG functions from working.

I have the same problem for months now (also the search function in my order is broken). Wrote to support when I needed a refund some weeks ago. I got the refund in my GOG wallet three days later, but never got an answer about the broken stuff in my account. It still doesn't work.

Got the problem solved folks. I had to login using the Brave browser because my versions of FireFox and Chrome are so heavily locked down with security features that they were interfering with GOG's refund page. Got the refund requested.

I dug a little deeper into why the game wouldn't start. It was actually trying to but because I'm not a Galaxy user(and the game exe EXPECTS to find Galaxy) it crashes when it does not find it. The exe makes calls to " Galaxy.dll ", " gog.gml.dll " and " steam_api.dll ". When I removed those dll's, the game got further and I saw a title screen, but then it swiftly crashed to desktop. Really kinda silly for the devs to make those assumptions and build an exe that way. It should be coded to "ignore if not found" and jump to the next routine without crashing.