It's been 43 years since I've lived in German-speaking Basel.
German is a "category 2" language, where "category 1" is the easiest to learn as an English speaker (Spanish being one of them). Category 2 is just a slight notch harder because it is a little more complex. The hardest categories include languages that are very distant to English and not related at all, like Mandarin and Japanese.
Let me add this. When you know one foreign language, it is much easier to get another one going. Once your brain has learned how to rewire itself around another language, it is much easier to do it again. Your brain learns how to map new concepts along those same pathways. Even more importantly, you've learned how to efficiently learn another language by that point.
My first foreign language was Greek. That led easily to German, Spanish, French, Latin, etc. But here's the clincher. Don't think that just because you've learned a language you're done. You have to maintain it. German is not a language you get "fluent" in and then keep it forever. You have to shore it up or it'll be lost.
The ideal would be to speak German with someone who is fluent in the language, that sort of thing. That's virtually impossible for me except when I'm traveling in Switzerland. Otherwise, I use the method of talking to myself to reanimate my German after almost 5 decades of not speaking that language every day.
How about you? What languages are you trying to learn? What online resources have you found most helpful? Do you have a native speaker to converse with?