Donnie,
That isn't an error that actually stops anything it is more a warning message. it just means the repo doesn't support i386 arch. which it doesn't.
If you would rather not see that error you can update the string in the repo line to include [arch=amd64] between the deb and the repo URL. if you have the [signed-by=/usr/share/keyrings/salt-archive-keyring.gpg] there just make that [signed-by=/usr/share/keyrings/salt-archive-keyring.gpg,arch=amd64]
Also, if you have 18.04 you shouldn't be using the 20.04 repo. there is a 18.04 repo. If you don't know what version of ubuntu you are on check /etc/lsb-release