Do not touch any interfaces defined in /etc/network/interfaces

/etc/NetworkManager/NetworkManager.conf

[main]
plugins=ifupdown,keyfile

[ifupdown]
managed=false

Specify interfaces to ignore:

/etc/NetworkManager/NetworkManager.conf

[main]
plugins=keyfile

[keyfile]
unmanaged-devices=interface-name:wlan0mon
unmanaged-devices=mac:xx:xx:xx:xx:xx:xx

nmcli con reload