What's the cause of the 'unmet peer dependency' messages?

Well, we’ve got a repeated tag somehow and its stopping the app from rebuilding, which i can fix by following this guide:

…but i can’t enter the app to fix it as its not running and won’t start or rebuild.

I was thinking that it might be due to those errors, and because our Docker and Ubuntu are a bit dated.

I guess i’m going to try and spin up a new Discourse on a new droplet, install Discourse and then restore our latest backup into it via command line so i can hopefully fix the repeated tag in the DB and reload the app.