@AstroNut 

Hi,

Actually, these are two separate issues that are not related to each other.

If your particular T3U Plus is designed for use in Europe (check if the label on the T3U+ has the letters "EU" on it), then it does not support the 5 GHz band U-NII-3 that comprises channels 149 to 165. 

However, Wi-Fi hotspots of smartphones do usually broadcast on exactly those channels.

As you've mentioned, there is no solution to this problem other than getting another Wi-Fi dongle that supports this particular 5 GHz band (like a T3U Plus labeled with the letters "US") or getting another smartphone that broadcasts its hotspot on a 5 GHz band that the T3U Plus "EU" can work with.

The problem of USB Wi-Fi adapters using certain Realtek chips not switching to USB 3 mode is another matter.

  @AstroNut 

I don't have the original packaging and the tiny text on the metal part of the usb plug doesnt have either EU or US on it.

I did a test - I connected it to a Linux VM on VMware workstation Pro - and it connected on the 5ghz band - Channel 149, but it is recognised as usb2 device.

  @AstroNut 

Ok, then theoretically your T3U Plus should also be able see that hotspot under Windows.

By the way, you also mentioned a router. Does the router also utilize channel 149? If yes, then can you configure the 5 GHz network of the router to use channel 36 instead and then check again if the T3U is able to see it?