If I insert a PowerPoint slide, GenCG doesn't load anything
After going through GenCG -> Insert -> PowerPoint slide, GenCG will first ask if you would like to import the file as a 4:3 or 16:9 aspect ratio. Once selected, GenCG will flatten and save each slide in an image sequence and save them next to the original PowerPoint file.
From here, go to Insert -> Image Sequence in GenCG, open the first image in the sequence, then all PowerPoint slides will import successfully.