Upgraded to 13 and lost a customized option

Sometime, a ways back, I added a button on the "operations" bar that dropped down into a list of all "Tab Groups". One one of my computers, the upgrade from 12->13 dropped this button, and I can't figure out how to recreate it.

Here's what it looks like

When I select "Customize" on the "Operations" toolbar, and right click the button I get this

When I select "Edit..."

I captured these screenshots from the computer that didn't lose the option. Now if I can just figure out how to recreate it...

While in Customize mode, drag it to a folder to create a file representing the button/menu.

Copy that to the other PC and drag it to the toolbar while in Customize mode there.

(You'll probably also find the button still exists on the other PC, in a backup of the toolbar. Directory Opus 13 - Tips for Upgrading from Opus 12 [Directory Opus Manual] has more detail.)