png to mpo conversion is a raster graphics export, typically used for making 3d stereoscopic images. You can find specialized utilities for making such stereoscopic images, although .jps is probably the more popular format for that. Still many these tools support MPO format as well and the same can also be achieved with Photoshop.
You can find guides and tutorials about making such '3D' images on the Internet, especially on YouTube.
Updated: August 30, 2023