Got only PART of the problem resolved by going to View/ Layout/ folder Pane Columns and ticking that. It brought back the mere "count" of messages in each folder but not the crucial determinant of action desirable which is the aggregate SIZE of all the emails in the folder. Unless a folder is consuming unreasonable amounts of disk space in the multi megabytes, there's no reason for me to fuss with it. The message count alone is virtually irrelevant. Thus far I have not been able to get the information that I actually need which is the SIZE of the entire folder.

ROTFL :) some days I'm a whole bunch slower than other days. This is one of those "slower" days. On my alternate computer which still has v36.1.0 installed with Extra Folder Columns add-on, I noticed the little hoochee icon at the right of the Total and Size columns that Extra Folder Columns was providing. Looking at my newly installed v45.1.0, I saw the same little hoochee icon, clicked on it, and voila! I got back my most important to me for administrative purposes SIZE column. Indeed it is true that the "Extra Folder Columns" functions have been made implicit as advertised and that the add-on is no longer useful and can be removed. Can even dispense with the number of messages if I want to.