As a alternative option, there is a free program called "System Transparency" that could accomplish what you want. In Windowblinds, the version I have, there is a feature called "Modify Style", click on that, then click on transparency, and you can make everything transparent by moving sliders partially to the left. So you have 2 options there. Hope this helps!    

Here's a link:

https://www.mediafire.com/file/5k9cvxhomqa97ju/System+Transparency.rar/file

Neone6 has used the above in connection with his various WB skins. 

If that link is concerning, here are a few other alternatives:

https://www.thewindowsclub.com/how-to-make-windows-transparent-in-windows

Glass2K is one of the options listed in the last link. I think I have a version of it on one or both of my 2 laptops that I rarely use. Take care and have a great day! 

That might be the reason, though I fail to see why you can't have transparency on a VM. Seems to me that there is something else going on. I am not an expert on virtual machines, but it could be a issue with your guest, and not the VM, try looking into your guest's window manager properties. Another possible problem area could be your graphics drivers for the VM. I do not have any other possible insight on this, since I don't use virtual machines. Hopefully we can get this resolved soon.  You might want to try another VM, such as VM Ware, or Windows Sandbox, and see if there is any difference with those.   

Thanks, I'll try that. Seems you're saying not all skins can be made translucent. It does seem that this setting is somewhat obscure - I've noted a number of questions related to it (including the links I cited).

Yesterday I finally saw a blur effect with WB in Win 10, but the effect was minimal.

I've been using Curtains (not available Win 11) and that works well- I prefer partial transparency (translucency).

Two other disadvantages of WB vs Curtains:

a. Curtains handles Store apps much better.  With some apps WB appears to apply a title bar as the app loads, then that disappears.

b. There are programs that add buttons on the title bar (e.g. Actual Window Manager). This is fine with Curtains, but the buttons (by default) are just above the top edge of the title bar when using WB.

I'm left wondering just what I do if forced to move to Win 11.

I've tried disabling blur on Win 11 (VM) using two different skins. No change to the titlebar.