With a small Bash script you can save some time, to set your Wi-Fi interfaces into Monitor Mode.
The aim of this tutorial is to set the Wi-Fi interface into Monitor Mode.
Install (or ensure they are installed) following packages.
# update system (optional)
$ sudo apt update -y && sudo apt upgrade -y
# install optional packages (optional)
$ sudo apt install -y wireless-tools
# install needed packages
$ sudo apt install -y curl
# change into home directory
$ cd ~
# download bash script
$ curl -L https://raw.githubusercontent.com/Lupin3000/Raspberry-PI-Tutorials/main/Goodies/BashMonitorMode/monitor-mode.sh -o monitor-mode.sh
# set file permissions
$ chmod u+x monitor-mode.sh
# show help (optional)
$ ./monitor-mode.sh -h
# enable monitor mode
$ sudo ./monitor-mode -i wlan1