I was annoyed by this:
$ sudo apt update … All packages are up to date. N: Skipping acquire of configured file 'main/binary-i386/Packages' as repository 'https://repo.pureos.net/pureos green InRelease' doesn't support architecture 'i386'
This is how I fixed it:
sudo dpkg --remove-architecture i386
For more info on that, I wrote a blog post as I was trying to figure it out.