I have a few questions about series (Twd and Alice in Borderland)?

Alice in Boderland:

Niragi still alive? At the end of the first season it looked like he died, but I just watched a Yt video about him where some in the comments said he was still alive. They knew that from the mangas / comics. Is that correct? Are the books also available in German or at least in English? I only found some in Japanese and French.

The Walking Dead:

Have you already known the release dates for the new episodes on Netflix? There's something different everywhere on the Internet. And is it worth watching these other series (Beyond the World and fear the Walking dead or whatever)?

I didn't watch Beyond the world, but everything The Walking Dead-related is worth it for me. So too is Fear The Walking Dead. But it depends on whether you prefer to wait a few months or years, or where else, where these seasons and series for The Walking Dead already exist, you want to pay more money. Personally, I will wait, even though I can no longer do it because I'm addicted to xD.

No, unfortunately there's no release date and you can't be 100% sure.

Have you already known the release dates for the new episodes on Netflix?

Exact dates are not known. In previous seasons, there was always about a year between the first release of Episode 1 on Sky and the release of the entire season on Netflix. With the additional episodes of season 10, it will probably be similar. From TWD, even episode 16 is missing from Netflix.

And is it worth watching these other series (Beyond the World and fear the Walking dead or whatever)?

TWDWB generally failed the audience. You can really save yourself the series. Opinions differ at FTWD. You can look at it, but it doesn't have to be. The mother series is definitely the best.

Fear TWD: The first seasons were worth it. Then at some point the style changes, so I didn't look any further. When exactly that is, I can no longer say.

World Beyond: The main story is muh, but you learn a little bit about the background. (Attention post-credit scene!) That's why I stayed with it.