The only ico to vst conversion that makes sense is export of graphics from various icon files (.ico) and save these images in one of the many possible raster image formats, for example Truvision Targa images (.vst or just .tga).
As far as we know, there is no fundamental difference between VST and TGA files, just different extension. Which means you can find more options under ico to tga conversion entry.
Updated: November 3, 2023