Long time ago I burned 8.6.1 on a DOK and ran: sudo apt update with not problems.

Now I tried the same and got several problems.
1. I had to remove /etc/apt/apt.conf.d/00knoppix

2. I had to run: sudo RUN echo "deb http://security.d
ebian.org/debian-security bullseye-security main contrib non-free" > /etc/apt/

3. I had to run
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6ED0E7B82643E131

Now I got:
The repository 'http://security.debian.org stable/updates Release' does not
have a Release file.

In my opinion - big mistake.
Why can't I use a previous knoppix version ?

I did the same with centos 7.2 (for example) which is also old.
Works like a charm.

All I'm trying is to install grub-efi. Till now I spent several hours on a quite simple installation which should work.

Thank you,