Activity Monitor columns missing My Activity Monitor does not have any columns that show more details about each process.

I've already ensured that under "View" in the menu bar, the relevant columns are enabled.
You can reset your Activity Monitor settings by quitting Activity Monitor, and then  deleting the preferences file, and any preferences lock files, and then re-opening the app.
Open Terminal and paste in the following command:
rm ~/Library/Preferences/com.apple.ActivityMonitor.plist*

(Note the * at the end to delete com.apple.ActivityMonitor.plist.lock and com.apple.ActivityMonitor.plist.)
Hit enter, and reopen Activity monitor - the columns should now be present.