I tried some basic stuff, I told you that needs time and packet capturing not an hour remote to your computer with no access either.
People need to understand how it works. It's not a "protection" you set and forget, or simply add one.
sudo -s
apt edit-sources
This is what I used inside the sources.list to update to the latest one bullseye
deb http://deb.debian.org/debian bullseye main contrib non-free
deb http://deb.debian.org/debian bullseye-updates main contrib non-free
deb http://security.debian.org/debian-security bullseye-security main
deb http://ftp.debian.org/debian bullseye-backports main contrib non-free
And then you run the above command.
@Elviuxx, I removed your topic from Private Servers (live). Please don't make double post. Once your server goes online, use the report section to ask a mod to move this topic to Private Servers.