Well, its the combination of Operating System, video card drivers (software) and and the card itself that is the issue. There are a lot of variables at play. Its not a question of supported/unsupported from my perspective, more a question of how the combination can process the graphics API, and if it does so correctly. Something in the mix is causing the breakage on the font textures. Is it fixable? Maybe so, possibly not. We are kind of at the mercy of these components working together.
There a couple of other flags that can be tried. Though they specify Direct X and I don't know if these are going to be non-starters for this.
Potential Flags are:
-force-d3d9 Make the game use Direct3D 9 for rendering.
-force-d3d11 Make the game use Direct3D 11 for rendering.
-force-opengl Make the game use OpenGL for rendering, even if Direct3D is available.
I doubt the 11 would work as the card itself only supports up to DX10, but you might try the 9
Unfortunately, the card is 10 years old and its capabilities might just not be up to modern API calls and the memory is low.
Also, if there is some sort of "Control Panel" for the video card there are possible options you can perform. These sorts of things allow you to make adjustments inside the card and that helps.
You might cycle between the 32 bit/64 bit versions if you have not done both, though I would not anticipate this changing the situation. But you never know.
Regarding your support question again. If you don't think you can get it working to your satisfaction and want to refund it, itch has a refund policy. https://itch.io/docs/legal/terms I would think this would fall under "technical issues" and you have worked with me on it. I always hate to go that route as my goal is to keep people playing this classic game, but if this is the only component combination you can readily use I am afraid you may have to go that route. It is not my goal to take your money and run. ;>