$ sudo apt update
Hit:1 http://nova.clouds.archive.ubuntu.com/ubuntu focal InRelease
Get:2 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]
Get:3 http://nova.clouds.archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]
Get:5 http://nova.clouds.archive.ubuntu.com/ubuntu focal-backports InRelease [108 kB]
Ign:4 https://www.virtualbox.org/virtualbox/debian focal InRelease
Err:6 https://www.virtualbox.org/virtualbox/debian focal Release
404 Not Found [IP: 137.254.60.32 443]
Reading package lists... Done
E: The repository 'http://virtualbox.org/virtualbox/debian focal Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
答案1
/etc/apt/sources.list您的或中的条目/etc/apt/sources.list.d/...不正确。应该是
deb [arch=amd64] https://download.virtualbox.org/virtualbox/debian focal contrib
域名是download.virtualbox.org，不是www.virtualbox.org。