PNG can preserve transparent pixels, while JPEG cannot. A transparent logo may look correct over a checkerboard but disappear over a dark or matching destination. A solid background fixes the compositing choice into every output pixel.
Transparent mode keeps the canvas alpha channel
VectorPNG clears a fresh canvas and draws the SVG without an opaque fill. Empty regions remain transparent in the encoded PNG. The checkerboard is only a preview aid; it is not written into the file. Inspect the result over the real destination colour.
Solid mode fills before drawing
White, black or one custom #RRGGBB colour fills the complete canvas before the vector is drawn. Semi-transparent SVG pixels blend against that colour and become opaque in the result. Changing the background clears the previous Blob so stale output cannot be downloaded.
Verify the receiving workflow
Open the PNG in the software that will use it and compare the important edges, text, colours and transparency with the source. Browser engines can shape fonts or colours differently and PNG stores fixed pixels rather than scalable geometry. Keep the SVG as the editable source; use the raster export only for the declared destination size.