mpg3 to ogg conversion might as well be a typo for mp3 to ogg conversion, but both of these are actually doable. In both cases it's audio conversion, just with different input format. While MP3 format is supported in pretty much any software, this might not be the case for .mpg3 files, although some sources claim it's pretty much just renamed .mp3 file.
Updated: August 21, 2023