Why don't flags show up in Big Sur?

If using the " Column View " in Apple Mail that is correct - the Flag Column is not there by default.

To enable Flags Column - right click " Subject : which will bring up a Sub/Menu and Enable Flags. Now that column should appear.

Hello WallyBertone, 

Being able to view email flags is a great feature of the Mail app on your Mac, and you’ve come to a wonderful place for help. You mentioned not being able to view the flags. Are you seeing the option to flag emails and to view the Flagged email folder? If so, there is a section titled Show flagged emails in the following article that may help. 

Flag emails in Mail on Mac

If you’re able to view the flagged emails, but unable to see the option to flag an email in the toolbar, you may have to right click on the toolbar where you see the option to send an email, forward an email, etc. Then click on Customize Toolbar. The window that appears will give you the option to adjust the layout of the toolbar, along with add and remove items as you desire. 

Have a great day!

We appreciate that clarification WallyBertone. 

Next to the flag icon are you able to click the down arrow to choose a different color for the flag? If so, is the email successfully marked? Also, have you noticed if this issue occurs when logged in to a different user account on your Mac? If you don’t have another user account to test this issue with, you can create a test user using the steps in the following article. 

Set up users, guests, and groups on Mac

When creating a test user account make sure it’s set as an Admin account, and let us know if the issue continues in that user. 

We look forward to the results!

Welcome and Thank you too :-)