I might have missed it, does this Window button's properties dialog
https://docs.xfce.org/xfce/xfce4-panel/4.12/tasklist still exist for Xfce4 - 4.14?
On my MX-16 install I was able to bring it up by clicking on "Window Buttons"
(it didn't have a icon) of the Xfce Settings screen/dialog. I can't tell which package or app provided it.
On MX-16 I use it, in the Behaviour section I change the window grouping from "never" to "always". I would like to do the same on MX-19.
I do see that there is a 4.14 page here:
https://docs.xfce.org/xfce/xfce4-panel/4.14/tasklist, but again I can't tell which package or app provides it, I don't see a "Window Buttons" item/icon on the MX-19 Xfce Settings screen.