Exactly. There’s a minimum 4 weeks that can be increased in the employment contract. Going up to 3 months is not rare, depending on the industry/type of job.
And it works both ways, so if the employer wants to fire you, the same notice period applies.
I had a very good experience with Honeypot (https://www.honeypot.io/en/). It’s Europe only, so not sure about the legal aspects of working from the US, but Germany have recently did some changes to laws related to work visas specifically to attract tech workers, so it shouldn’t be that hard. You speak German, so that’s a big plus.
It’s a “reverse” job search, in the sense that you create your profile/CV and companies apply to you. After creating your profile, you do a short call with a recruiter, that helps you adjust it to the type of job you are looking for.