I found answers at Hardware Central

"Load BIOS Default" is used to load a set of BIOS values to be used for troubleshooting. These are non optimal values that disable all high performance features of the chipset.

"Load Setup Defaults" is the standard BIOS settings that will work best with most configurations. Experienced users will adjust individual settings and customize the system to their needs.

and at manualslib
https://www.manualslib.com/manual/791561/Soyo … kd.html?page=33

Load BIOS Defaults & Load Setup Defaults
These two items both set the BIOS settings back to their default values.
The difference between the two is that BIOS Defaults loads the most conservative values, meaning that it is best to load the BIOS defaults whenever you are experiencing problems; on the other hand, Setup Defaults setting are optimized for speed and are usually the best settings to load.

Big thanks 😁