I will start by mentioning that initially, I had the Windows 11 Pro transparency setting off. Accessability>Visual Effects>Transparency Effects.
Changing the 'auto colour' and/or 'texture' does not affect the transparency of the Start Menu. It's still completely solid; but, as mentioned before the Taskbar Transparency is working as intended.
Now, turning ON the Windows transparency setting mentioned above DOES affect the Start 11 Menu. The Start Menu transparency effect in the Start 11 settings will now work as intended and I can adjust the % of the effect.
However, isn't there always a 'however'... lol, turning ON the Windows transparency setting turns OFF the Start 11 transparency effect, that previously worked for the Taskbar, even with the Start 11 Taskbar setting set to ON.
So, with the Windows setting ON, the Start11 Start Menu transparency works but, the Taskbar transparency does NOT work. With both Start 11 settings set to ON.
With the Windows setting OFF, the Start 11 Start Menu transparency does NOT work, but, the Taskbar transparency DOES work. With both Start11 settings set to ON.
There is a conflict between the Windows transparency setting and the Start 11 transparency settings.
Cheers.