RouterOS on Proxmox

I have installed RouterOS (ver7.16) on Proxmox. I have a TP-link T4U USB device connected to the PC running Proxmox. I added the USB device to the RouterOS VM and I can see the USD device in WinBox under System->Resources->USB. It is listed as a Realtek 802.11ac NIC. How can I use this device to set up an access point? The device is not listed in the Interface List

I do not understand what you are asking for.
Typically , you do not use or need a USB interface when setting up a Mikrotik device to talk to something else.
I would suggest adding some additional information and a simple network drawing so that we can better understand what you are trying to accomplish.

@FredRoot - You can’t manage USB network devices directly from CHR. You need to set up and manage the TP-Link T4U from the host OS first, then add it to Proxmox like a regular network device. Check this out: add usb network device to proxmox

Thanks @Larsa and @TomjNorthIdaho, I was under the impression that I could setup the USB WiFi device from RouterOS because the OS did detect the USB device. I see I have to do some additional research.

ROS did detect USB device and it even knows the name of it. But that doesn’t mean that ROS has driver for it (it very likely doesn’t), the name comes from pci.ids file, which is local copy of pci ids repository.