I use mail in the column view and in Monterey on a Mac Mini (2020), I cannot find a way to add columns for flags and for attachments. This is really frustrating and I may have to switch to a different mail client if I can't solve it.
In the Mail Sidebar hover the cursor to the right of Favourites and click on the plus sign and add Flagged:
In the Mail Sidebar hover the cursor to the right of Favourites and click on the plus sign and add Flagged:
In the Header >> " Subject " and Right Click. A Sub Menu will appear. Choose and enable Flags
refer to below
Moneteray mail flags and attachments
