No way to change forum password? Primary Forum Email is good for nothing?

I don’t see anywhere to change password?

And when I change Primary Email, it doesn’t use this email as login?

I guess it’s tied only to your Steinberg ID

As @LoveGames says, you can change your email address or password on the Steinberg ID page:

https://id.steinberg.net/user/ui/en/user/sign-in-and-security