I'm also German and my mother is similar, albeit less extreme. She is still nice to me and somehow genders me correctly when texting me but doesn't care for my preferred pronouns when we talk in person. I don't want to go no contact because I'm on good terms with the rest of my family (they mostly don't care and accept my identity without much fuss) so I cope by not interacting with her a lot when we see each other. I see my family every two months or so and when I do, I don't sit next to her, only talk the necessities etc. She still manages to misgender me every time to speak. It hurts, but no contact is not an option for me so I just endure it. I prepare visits to family by pampering myself and always plan quality time after a visit. I refuse to meet her 1-on-1. It's not ideal, but okay for me.

I don't know what it's like with your dad, but my mom is just a very stubborn person that doesn't adapt well to change. My sister's husband is vegan and has been for years and she still cooks meals with meat and dairy in them when he comes over. She just says he should bring his own food to family dinners. To me, this confirms that my mom isn't like this to me (just) because of my identity, but also/mostly because she can't handle change.

Edit: Oh and also it's gotten slightly better the more I visibly feminize. I think she's a bit of a transmedicalist without knowing the term, GRS will probably help as well.