'apt-get update' stopped working and gives unsigned repo message. any ideas how this happened?

solved: apt-transport-https must have been corrupted or some other similar issue. (i am not sure if this previous sentence actually had anything to do with the successful repair, but i did it, so i am documenting) then used apt-get purge remove apt-transport-https, and followed the checked answer to complete my repair of the issue.

original: I am running ubuntu 21.10 and apt-get update stopped working, here is the output:

sudo apt-get update
Hit:1 http://us.archive.ubuntu.com/ubuntu impish InRelease
Get:2 http://security.ubuntu.com/ubuntu impish-security InRelease [90.7 kB]
Get:3 http://us.archive.ubuntu.com/ubuntu impish-updates InRelease [90.7 kB]
Hit:5 http://us.archive.ubuntu.com/ubuntu impish-backports InRelease           
Err:4 https://dl.bintray.com/etcher/debian stable InRelease
  403  Forbidden [IP: 52.42.128.10 443]
Reading package lists... Done                  
E: Failed to fetch https://deb.etcher.io/dists/stable/InRelease  403  Forbidden [IP: 52.42.128.10 443]
E: The repository 'https://deb.etcher.io stable InRelease' is not signed.
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.

Any ideas why this would have suddenly started happening? And how to repair it?

Solution 1:

The error message refers to the Balena Etcher PPA that has been deprecated.

Remove the old PPA amd add the new one according to the instructions linked above and reproduced here:

curl -1sLf \
'https://dl.cloudsmith.io/public/balena/etcher/setup.deb.sh' \
| sudo -E bash

If you have Balena Etcher already installed it'll will be upgrade alongside the other updates.