We tried to provide migration instructions for the most common customization patterns, like the ones that modified the post-stream.
It’s harder to write a more comprehensive guide because pretty much anything could be done using widgets, so the remaining customization needs to be converted to components on a case-by-case basis.
I’m watching these topics and we’ll try to answer questions posted here to aid those that still need to migrate.
I’ve looked briefly at the code that looks like it’s triggering the deprecation in your forum using the browser console, and it seems like it’s the following line:
const { iconNode } = require("discourse-common/lib/icon-library");
let iconsjira = iconNode('icons-jira');
iconNode was used only by widgets, and now it’s a noop function. In your code it doesn’t appear this variable is being used, so it should be safe to just remove these lines.
Let me know, if you need more help.