looks like is not compatible for >= 20.04 . I installed a new Ubuntu 20.10 and got the following:
sudo add-apt-repository -u ppa:archivebox/archivebox
apt install archivebox
More info: https://launchpad.net/~archivebox/+archive/ubuntu/archivebox
Adding repository.
Press [ENTER] to continue or Ctrl-c to cancel.
Found existing deb entry in /etc/apt/sources.list.d/archivebox-ubuntu-archivebox-groovy.list
Adding deb entry to /etc/apt/sources.list.d/archivebox-ubuntu-archivebox-groovy.list
Found existing deb-src entry in /etc/apt/sources.list.d/archivebox-ubuntu-archivebox-groovy.list
Adding disabled deb-src entry to /etc/apt/sources.list.d/archivebox-ubuntu-archivebox-groovy.list
Adding key to /etc/apt/trusted.gpg.d/archivebox-ubuntu-archivebox.gpg with fingerprint 2BCCD744CC1AD54C9DC77DE8C258F79DCC02E369
Ign:1 http://ppa.launchpad.net/archivebox/archivebox/ubuntu groovy InRelease
Hit:2 http://archive.ubuntu.com/ubuntu groovy InRelease
Hit:3 http://archive.ubuntu.com/ubuntu groovy-updates InRelease
Err:4 http://ppa.launchpad.net/archivebox/archivebox/ubuntu groovy Release
404 Not Found [IP: 2001:67c:1560:8008::19 80]
Hit:5 http://archive.ubuntu.com/ubuntu groovy-security InRelease
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/archivebox/archivebox/ubuntu groovy 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.
root@archivebox:~# apt update
Ign:1 http://ppa.launchpad.net/archivebox/archivebox/ubuntu groovy InRelease
Hit:2 http://archive.ubuntu.com/ubuntu groovy InRelease
Hit:3 http://archive.ubuntu.com/ubuntu groovy-updates InRelease
Hit:4 http://archive.ubuntu.com/ubuntu groovy-security InRelease
Err:5 http://ppa.launchpad.net/archivebox/archivebox/ubuntu groovy Release
404 Not Found [IP: 2001:67c:1560:8008::19 80]
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/archivebox/archivebox/ubuntu groovy 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.
root@archivebox:~#
Would be nice to get this fixed.