Need to go to your Motherboard's QVL List to see if your specific RAM Memory is supported at that speed.
The QVL List will indicate how many DIMM Slots you can populate to be supported and the maximum speed supported by your specific RAM Module and whether you can OC the RAM.
If your RAM is not listed on the QVL List than you need to go to G-Skill Support and asked them at what speed their RAM Memory is supported on the Asus Motherboard with the Ryzen 3990X processor.
According to Asus CPU SUPPORT LIst concerning the Ryzen 3990X it doesn't support OC : Prime TRX40-Pro CPU Support | Motherboards | ASUS USA
If your G-Skill stock speed is 3600 Mhz then that is the maximum speed it should run with your processor.
Here is the QVL List for G-Skill for your Ryzen 3990X. It doesn't list any RAM Memory Modules of 16 gbytes (8) or 32 gbytes (4) which both total 128 gbytes of RAM Memory: Prime TRX40-Pro Memory | Motherboards | ASUS USA
I in inputted G-Skill RAM Memory of 3200 Mhz and found that it is compatible in 8 DIMM slots for 128 gybtes of RAM:
You will need to open a G-Skill Support ticket to find out if your RAM is compatible with your Motherboard and how many DIMM slots it will support and what speeds.
It is possible the motherboard doesn't support 100% 16 gbyte or 32 gbyte RAM Modules.
Install just one RAM Module and see if it will work at 3600 Mhz. If it does then most likely it is only supported on a certain amount of DIMM Slots and not the full 8 DIMM Slots.
