I just upgraded Discourse and do recieve the following message in two out of my four instances:
[Admin Notice] One of your themes or plugins needs updating for compatibility with upcoming Discourse core changes. (id:discourse.fontawesome-6-upgrade)
As I do not have a plugin or theme component with that name and also because FontAwesome is a core feature (in my eyes), I do not know what I can do here to solve this information.
No worry! This warning means you have either a theme component or a plugin that uses an old font-awesome icon name. You have nothing to do; it’s up to the authors to update their plugins/components.
Discourse recently migrated Fontawesome from v5 to v6; a few names must be renamed. In your case, I looked at your forum and saw map-marker-alt (new name is location-dot). It’s likely from Locations Plugin.