The 2.X GHz is obviously working, but I want the 5GHz, in which the adapter is not detecting (while other devices within the vicinity are able to detect).
What is the operating system of your computer?
Please move it closer to the main router and check whether it can detect the 5GHz.
Besides, try to change the wireless channel of 5GHz and give it a go.
Note: You can use channel 36, 40 and 44.
Any updates, please let us know.