Solved Tiny 11 Display Resolution Problem

you could try coping the drivers from Win10 on to USB then in Tiny Win11 VM via the device manager update the drivers.
that way Tiny Win11 would have, hopefully, the required drivers for the VM to display 16:9.
i assume you have the VirtualBox extension pack installed.

also have you tried Gnome Boxes i always found that works better in Linux then VirtualBox ..

OK, I've finally resolved my display resolution issue.

I haven't set up a new VM for a long, long time. The last time was a Windows 7 install, which had been upgraded to Windows 10 quite a while ago. What I hadn't done this time was install the Guest Additions. Clearly I did this with the original Windows VM, but I sure don't remember doing it.

Anyway, I've installed Guest Additions for the both Tiny 11 and the Windows 11 custom VMs. Installing the GAs did the trick! Both VMs now make use of the full HD video capability of my monitor with no stretching or other types of distortion. It's a good thing, too. I may have already spent more time on this than I will spend running Windows software for a year ... maybe more.

Thanks again for the many suggestions which steered me in the right direction.