GNU/Linux Ubuntu 20.04 Installing D-Link DWA-131 C1/E1 Wifi/Bluetooth Driver Guide
Hi! The linked Tutorial shows you Step-by-Step How to Install D-Link DWA-131 C1/E1 Wireless N Nano USB Adapter Driver in Ubuntu 20.04 Focal LTS GNU/Linux.
And the Ubuntu Focal D-Link DWA-131 C1/E1 Wireless Driver Setup is based on the Realtek rtl8192EU Chipset Driver Installation.
Especially relevant, if you are Unsure about your Wifi Device Chipset then see: How to Get Wireless Adapter Info on GNU/Linux.
GNU/Linux Ubuntu 20.04 D-Link DWA-131 C1/E1 Driver Setup Guide
See: Realtek rtl8192EU Linux Driver Installation
Last, in case of Issue you may see: How to Update Linux Firmware!