Question BIOS shows 2x8GB RAM but OS shows just 8GB

Apr 18, 2020
System Specs:
Ryzen 7 2700X, stock speeds
Gigabyte x570 Gaming X, BIOS revision F12e (latest)
G.SKILL Aegis 16GB (2x8GB) 2400MHz PC4-19200, stock speeds
KDE Neon User Edition 5.18

For many of the tasks I do I need 16GB of RAM, however in the operating system I am capped at just 8GB. I have the memory sticks installed according to the motherboard manual (one in A2, one in B2), and in the BIOS it shows 16384MB. In addition, in MemTest86, it shows that I have two different 8GB sticks installed. However, in both MemTest86 and KDE Neon I only have 8GB available, which has been causing me lots of problems. Is it an issue of compatibility between the 2700X and an X570 board, or do I have defective hardware?