Cannot find wlan device (monitor mode) in device list / Linux mint

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Hello,

I switch my wlan interface (interface for USB/ Realtec 802.11n WLAN adapter) to monitor mode with the following commands:

sudo ip link set wlx74da38e2f0fa down 
sudo iwconfig wlx74da38e2f0fa mode monitor

iwconfig says that this was successful:

wlx74da38e2f0fa  IEEE 802.11  Mode:Monitor  Tx-Power=20 dBm   
Retry short limit:7   RTS thr=2347 B   Fragment thr:off
Power Management:off

However, I cannot find the device in the device list of Wireshark anymore!? How is this possible?

I use Linux Mint 18.3 'Sylvia' "Cinnamon 64-bit"

Thanks a lot, iago