Depends entirely on where in Europe you’re going - There are technically more countries where you’ll be able to use German, but it’s often limited to specific areas of them that are right next to Germany, so neither language is super useful for Europe in general.
You’ll have better results working on your feelings of being a dipshit who only knows one language - even if you learn a new one you aren’t going to be speaking the local language for a lot of the trip, but the locals will probably speak some English, so you’ll be doing a lot of communication with a mix of that and a translator app. Plenty of locals won’t speak any English though, or any other foreign languages, because like you they don’t have a need for a second language; neither you nor they are dipshits for not knowing how something you have never needed or used works.

If you live in the US, Spanish will be eventually helpful to you in many ways, especially in political organizing. Spanish is one of the major languages of the colonized world and therefore an enormous amount of excellent politics is happening in Spanish. Learn Spanish.

Spanish is cooler and sexier

Spanish might also be helpful in France because a lot of Spanish words are French words with O or A at the end

If we’re talking only Europe, I might actually say French, just because of how familiar Germans are with English. Most Europeans speak good English, but France is kind of an outlier there. In terms of overall usefulness, however, Spanish is hands down the more useful language to learn given how widely spoken it is in the world.

German is far more useful (in Europe) unless you’re traveling around Spain; the Balkans and Eastern Europe in particular will have a lot of German speakers, the low countries have plenty of German speakers, and of course the Germanic countries as well. That said, Spanish or German pale in comparison to English in terms of usefulness, and there’s very few instances outside of German countries (Switzerland, Austria, Germany, Luxembourg kind of) where somebody would prefer to speak German to you than English. If you’re planning on traveling to South America ever just learn Spanish instead, it’s far more useful globally and has way more speakers than German. It’s relatively easy to get by with just English anywhere in Europe that’s on the tourist circuit.

The only reason to learn German is if you intend to emigrate there. English and knowing key phrases in the country you’re in is sufficient in Western Europe.

You’ll almost certainly be fine with only English because so many people speak at least a little bit of it. You may have trouble in places that don’t get many tourists but translate apps are pretty good these days and you can download language packs usually for offline translation. If you’re going to go to South America having a bit of spanish will be way more useful because at least in my experience english proficiency is a lot lower there than in Europe. So if you want to learn a language I’d say go with Spanish instead of German. You’ll get more practice by sticking to it longer, it’s probably more familiar to you if you’re an American, and it’ll overall be more useful for the kinds of things you want to do.

People will almost certainly prefer speaking English to you outside Spain or the German-speaking countries, and also probably inside them, sadly. Just learn a couple of useful words per country as you travel, some places love that shit. Sounds like you are a little more motivated to learn Spanish, which counts for a lot, so I would go with that.

You speak english, so:

West of the former GDR border: spanish
East of the former GDR border: german

never learn german

Spanish in Italy, maybe France and Portugal. German in Eastern Europe.

As long as you don’t speak to boomers, most people should at least know basic English.

Only time I really needed to speak German in Germany was giving directions to a cab driver. I think pretty much everyone speaks English there except recent immigrants.

I’d also say French people outside of touristy areas are less likely to speak English than germanic peoples. I haven’t been to Spanish language countries. I’ve heard Spanish is close enough to Italian to be somewhat intelligible, but IDK, YMMV.

Depends where you’re going, neither will help much in France. Spanish is maybe a bit easier to be minimally functional in as a beginner.

I think it’s a good idea to learn the polite basic words of every country you visit.