How to change message list columns?

[DavidTCS]

How do I chnage the columns displayed in the message list?

The documentation I have found (at https://docs.roundcube.net/doc/help/1.1/en_US/mail/mailview.html) says "The columns displayed in the list can be adjusted by clicking the List Options icon in the leftmost column of the message list header.".

Another page I have found at https://squirrelhouse.biz/roundcube-mail-altering-displayed-columns/ shows an image of this (see first attachment).

But I don't see any column headings - for what I see, please see the second attachment.

This is Roundcube 1.6.12 with (I think) skin elastic.

How do I make column headings show, please? (and then, g=hopefully, I'll be able to see the "List Options" icon).