therein be the problem- you need to install the S3 Trio drivers for windows 3.1 onto the VM.
It's a huge PITA to find on the web... at least it was for me, so I'll attach them.
Basically, get them onto the VM; in a separate folder.
Then, with the windows setup program, select "have disk" for video; then enter the path to where you unzipped the files; it will then give you a number of options; choose one (personally I prefer the 24-bit colour options...)
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