Kubuntu - can not enter wifi credentials after adding external wifi card

My ethernet connection is quite unreliable (It uses powerline adapters) so I bought an external wifi adapter. I have plugged it in and run the command sudo ip address add 192.168.0.39/24 brd + dev enp7s0, and KDE has detected it. Unfortunately, it doesn't seem to realise it is a wireless network and therefore needs credentials. Where I could normally find a place to enter credentials (the network widget, system settings) there are none. KDE reports that the device is connected in the UI. How do I make it work out that it is wireless and therefore needs credentials?

Edit:

With ethernet plugged out, (USB) adapter plugged in:

$ ip address show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp7s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000
    link/ether 04:d9:f5:8a:f5:e0 brd ff:ff:ff:ff:ff:ff

With ethernet plugged in, adapter plugged in:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp7s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 04:d9:f5:8a:f5:e0 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.51/24 brd 192.168.0.255 scope global dynamic noprefixroute enp7s0
       valid_lft 863988sec preferred_lft 863988sec
    inet6 fe80::7eb1:eca2:96a0:fe5c/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

With just ethernet:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp7s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 04:d9:f5:8a:f5:e0 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.51/24 brd 192.168.0.255 scope global dynamic noprefixroute enp7s0
       valid_lft 863960sec preferred_lft 863960sec
    inet6 fe80::7eb1:eca2:96a0:fe5c/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

With nothing:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp7s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN group default qlen 1000
    link/ether 04:d9:f5:8a:f5:e0 brd ff:ff:ff:ff:ff:ff

lsusb, adapter plugged in:

Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 002: ID 046d:c31c Logitech, Inc. Keyboard K120
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 003: ID 1d57:32da Xenta 2.4GHz Receiver (Keyboard and Mouse)
Bus 001 Device 004: ID 0bda:b812 Realtek Semiconductor Corp. 802.11ac NIC
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

I'm not adding it with it plugged out because it's obviously the Bus 001 Device 004: ID 0bda:b812 Realtek Semiconductor Corp. 802.11ac NIC. There were no restarts between any of these changes.

Solution 1:

First of all, enp7s0 is likely not the designation of your wireless device. enpxxx is generally reserved for ethernet devices. Find out the correct designation with:

iwconfig

If, as we expect, you find 'No Wireless Extensions' then your external device hasn't claimed a suitable driver. Is your external wireless device a USB device? If so, please edit your question to show the result of the terminal command:

lsusb

Once we have more information, I will expand this answer to show the next steps.

EDIT: Your wireless device, 0bda:b812 Realtek Semiconductor Corp. 802.11ac NIC, uses the driver 88x2bu. With a working internet connection, presumably the ethernet, open a terminal and do:

sudo apt update
sudo apt install dkms build-essential git
git clone https://github.com/cilynx/rtl88x2BU_WiFi_linux_v5.3.1_27678.20180430_COEX20180427-5959
sudo dkms add ./rtl88x2BU_WiFi_linux_v5.3.1_27678.20180430_COEX20180427-5959
sudo dkms install -m rtl88x2bu -v 5.3.1
sudo modprobe 88x2bu

Your wireless should now be working. The KDE GUI, Network Manager, should announce that wireless networks are available, show you a list and offer to connect. After you supply the requested WPA2 password, you should be all set.

Kubuntu - can not enter wifi credentials after adding external wifi card

Solution 1:

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