Here's is another great video by Family History Fanatics. It is from 2017 using the old Gedmatch, but it is still relevant. You can still use the same tools on Gedmatch Genesis (One-to-one Autosomal Comparison). This one explains how different companies test different areas. You can see which particular segments are picked up on compared to the other, and what they missed. Because you're comparing your own genome, to your own genome, there is almost complete overlap. But segments painted in black are where they differ.