Building 21.02 for WNR2000v3

Can someone refer me to some documentation I should read to get up to speed on how to make my own builds of OpenWrt v21.02 for the Netgear WNR2000v3 (a 4/32 router)? This router is supported by v19.07.

I have Debian GNU/Linux on my computer, and I have all the build requirements installed.

There is a DEFAULT := n line in target/linux/ath79/image/, remove that and you can compile an image for your device. Do keep in mind you'll need to strip some stuff (like LuCI, and possibly PPP support as well).