Install updates Pub Key

[firenice03]

[member=49679]triwiwer[/member]

Also looks like a couple other errors once the key is accepted..
Remove the "old Ubuntu" repo

Code:

Err:10 http://old-releases.ubuntu.com/ubuntu focal-security Release
  404  Not Found [IP: 91.189.91.124 80]

and
The multiple repos configured multiple times

Code:

is configured multiple times in /etc/apt/sources.list

You could be able to edit the /etc/apt/sources.list as administrator (file manager)

- I'll check the key - are you on a corporate network or behind a firewall?




UPDATE..
See this link for other key servers vs. keyserver.ubuntu.com
https://www.duinsoft.nl/keyservers.php?t=en