dch is not included by default on minimal Raspbian installs; thus the "Building under bullseye, buster, or stretch" section should have devscripts added to the apt-get command:
sudo apt-get install build-essential fakeroot debhelper librtlsdr-dev pkg-config libncurses5-dev libbladerf-dev libhackrf-dev liblimesuite-dev libsoapysdr-dev devscripts