Ozimandeus: A made in USA tag would be helpful, but I think a tag for each country would serve the goal better. That way I can also ensure Canada, Mexico and Panama are also supported by my money.
Nobody is going to be 100% clean on this issue. You're going to find that almost everyone is going to be dirty somehow even if the developer is in Europe. They may use a US publisher or use US location services to translate their game to other languages. If they're not selling their game exclusively on GOG, they're doing business with US-based stores. Regardless of which storefronts they use, they're accepting purchases from US-based customers because they want our money.
Even GOG itself is going to fail the no US purity test. They still sell games with US developers, publishers, and/or localization. They accept purchases from US customers. GOG really can't afford to give up the revenue from doing business with the US.
Ozimandeus: I have no hatred of the USA. We have been friends my entire life - and in time, I think we will again. But I don't agree with your consistent choice of government, and your system's slide towards fascism has given me significant cause for concern (That's British for really pi**ed me off). As someone of German and English descent, my family has seen this pattern before, we know where it leads and its time for us to make a stand, even in some small way as making sure I only buy videogames made by a European developer (for now).
And that's another thing. People want to be r/AmericaBad, but the country is not a monolith. There are plenty of people here that hate our government far more than you ever could due to being impacted directly on things we didn't even vote for.
Also one of the absolute least ethical companies on the entire planet is Nestlé, which is based in Switzerland. Nestlé engages in aggressive marketing of infant formula over breastfeeding in developing countries, steals water, doesn't engage in fair labor practices, engages in price fixing, participates in deforestation, and routinely spreads disinformation about recycling. Every Nestlé product with chocolate is the result of child trafficking and/or slave labor. This company does so much evil all by itself that I'm sure that there's something that Nestlé has done that I forgot to mention.
And I'm not saying this as a WhatAboutIsm.
I'm saying good luck on that US boycott when it comes to games, but you should seriously boycott Nestlé. The company doesn't deserve a pass just because it is based out of a European country where the country itself is perceived as ethical.