Would you please do a screenshot of what you're seeing? Thank you.

Here it is.

I have never seen this in the message list pane. Are you using any addons?

Only Cardbook and sendlater. These (CB) appeared after the latest update. 128.4.3esr (64-bit)

Try disabling the addons and then see what you have

Turned them off then one at a time turned on. Then both turned on. No more (CB) in any accounts that I can find. Thank you.

Extra columns have suddenly showed up again but only on "sent mail". I turned both add-ons off and re-started T-bird. Turned them on and columns reappeared. Turned off add-ons and columns disappeared. Turned add-ons on and the columns stayed gone.

You can write-click on the header row and select/deselect columns (including the (CB) ones), but this is per mailbox so it can be laborious if you have several email accounts in TB.

I assume that CB is from Cardbook and that Cardbook gives you some way of managing its features.

You can copy and paste column and view settings from one folder to all folders in an account in one step. See the button on the far right of the message header toolbar.

The issue appeared in the regular inbox columns of each account.

Not sure how to mark the problem seems resolved. I had to go into each account and turn the displayed columns off. Fortunately, issue has not returned. Thank you all.