Thanks @bschaaf, that made me look at this in a bit more detail: I should have looked at the error messages a bit more thoroughly.
Regarding the URLs: I knew that this is the case for apt but I tried some of the others that look a bit more like complete URLs - Obviously those don’t work as well. Good to learn.
Maybe this helps anyone else stuck where I was stuck, so here’s the problem as I understand it:
The actual problem (which I didn’t see initially in the flurry of output of apt update) was a certificate problem with download.sublimetext.com due to (I assume) the recent root cert expiry at LetsEncrypt. To fix this, I needed to update the specific certificate packages in Ubuntu - Which didn’t work because apt update fails. To fix this I
- commented out the sublime source
- ran apt update and apt upgrade
- removed the comment
- ran apt update and apt upgrade again
And now everything seems to be in order.
Oh and @dllord, I just did that on this machine and got 4121.