Once set up, you’ll see an IP address for local area network access to your Xbox that you can use to remotely install apps onto your console via your PC. From there, it’s just a case of signing up for a Microsoft Developer Account for $19, connecting it to your Xbox and boom - you have developer mode on your Xbox.
To tee things off, you need to search for “Dev Mode Activation” on your Xbox app store, then install and open it.