It appears that the latest HWiNFO64 improperly reads the RAM speed of 6400MHz LPDDR5 as 400MHz. (Asus ROG FLOW X13)
Windows 11 Task Manager reads it at 6400MHz.
Is this because you're still trying to figure out the best way to read the live frequency?
Windows Task Manager cannot be considered as a reference source of hardware information.
Memory frequency can decrease when the system is idle. Try to put some load on the system and see if it increases.
If not, please attach the HWiNFO Debug File.