This article was sourced from: https://www.tomshardware.com/news/raspberry-pi-bootloader-network-install-beta-release
Raspberry Pi has released a new beta bootloader for Raspberry Pi 4 and 400 devices that enables a very interesting new feature; OS installation over a network. And being a beta version, Raspberry Pi is looking for help testing it out.
Right now the network install feature is a beta; but after all of the bugs have been ironed out we can expect to see this feature become part of the default bootloader for a future release.
Currently, to get a new OS onto a Raspberry Pi board; you need to either use the NOOBS software from a micro SD card; or flash the OS onto a micro SD card using the Raspberry Pi Imager software running on another computer. Network installation essentially runs the Imager in the board’s memory; allowing you to download and flash a new OS using an Ethernet internet connection.
To install the new bootloader, you’ll need to use the Imager on a Windows, Mac or Linux computer. We updated the Imager software for Windows to the latest available version, 1.7.1; and found there were three options available in the Beta Test Bootloader section; two for USB/SD booting and a new one, dated February 4th 2022, for network booting with a fallback to the micro SD card. Note that installing this bootloader appears to disable USB booting; but you can also use this process to return the Pi to booting from USB, by moving to the appropriate bootloader.
Use the Imager to flash the new bootloader to a blank micro SD card; then place the card in your Pi 4 or 400 and switch it on. A flashing LED followed by a green screen indicates a completed update. Put back your original micro SD card, and it should boot normally into your chosen OS.
To use the network install feature; you’ll need another empty micro SD card of sufficient capacity, and connect a keyboard to the Pi. Switch the Pi on with the blank micro SD card inserted, and you’ll get a network install screen. Hold down Shift for three seconds, confirm your intentions with a press of Space; and you’ll be asked to insert an Ethernet cable with the internet on the other end. Once your internet connection has been detected the Imager software will be downloaded; and you can use it in exactly the same way you would on a PC; Mac or Linux computer, choosing the OS that your Pi will use.
Raspberry Pi is asking for feedback on its new bootloader via its forums.