Do not post about the alpha/RC version of elm-upgrade on reddit, twitter, HN , discourse etc
That's already an issue about alpha.elm-lang.org being broken, changing it to point at package.elm-lang.org gets me further but the next set of errors are so unhelpful I'm giving up.
It's just telling you that it's pointless to post about issues on social media because the tool is in alpha and is obviously going to fail in many cases…
The document I linked too contains the language and std-lib changes between 0.18 and 0.19, for the rest you use new packages.
If you don't want to upgrade that's fine, but you're literally staring at the information on what to do.