There’s no gnome-shell-extension-dashtodock package for focal , but I did try with Dash to Dock from extensions.gnome.org, and could not reproduce the issue with it. I tried with the default settings, as well as after recreating the look & feel of Ubuntu Dock as much as possible.
Dash to Dock has customizable action for the scroll (to either switch workspaces or windows, or to do nothing), and all of those also worked just as expected.
I also noticed that using the two finger scroll function of the touchpad on my laptop does *not* trigger this (whereas using the mouse on it does).
*  https://packages.ubuntu.com/search?keywords=gnome-shell-extension-dashtodock