Those are bitmap (raster) image file formats that can not contain vector shapes. The "Convert to Curves" feature in Affinity only works on vector shapes (rectangles, circles, the many special shapes like stars, & so on). What you want is often called bitmap tracing, & is not supported in Affinity.
It is an often requested feature but the staff have said it will not appear in an update to version 1.x. So it is at least a year away & probably part of a paid upgrade to version 2.x if/when it is implemented.
