AC600 wifi 5ghz dongle or Realtek Semiconductor Corp. 802.11ac NIC on Ubuntu

That's a BlueShadow AC600, which uses an RTL8812AU. There's a pretty decent driver available for this from the aircrack-ng team available on GitHub, and it's not too difficult to get it going.

From a terminal, if you don't already have dkms on your machine:

sudo apt update
sudo apt install dkms

Now we can clone the 5.6.4.2 branch, which is one of the more stable versions:

git clone -b v5.6.4.2 https://github.com/aircrack-ng/rtl8812au.git
cd rtl8812au
sudo ./dkms-install.sh

From here the driver will install and your WiFi dongle should be picked up.

I have the same adapter. These commands fix the problem:

sudo apt update
sudo apt install build-essential git dkms
git clone https://github.com/brektrou/rtl8821CU.git
cd rtl8821CU
chmod +x dkms-install.sh
sudo ./dkms-install.sh
sudo modprobe 8821cu