I keep seeing this response over and over in this forum.
Instead of blaming the new users, why doesn't someone just remove the "New Topic" button from the https://forum.arduino.cc/ page?
The only reason users are posting in the unspecified category is because there is a big button on the main page that says "New Topic," which posts directly to the Unspecified topic. Just remove that button already...
If the user attempts to publish the topic without explicitly selecting a category from that "category" menu, the forum software will block the publishing with a "An error occurred: Category can't be blank" dialog:
We created the #using-arduino:uncategorized category because previously when people arbitrarily chose the first category on the list, the miscategorized topics ended up in the #using-arduino:ide-1-x category where it was less likely that the moderators would spot them since they were mixed in there with topics that are actually about Arduino IDE 1.x.