Can someone explain u-boot

I have just installed ubuntu focal server on a rockpi4 c+ board and I am reading through the documentation.

I am somewhat confused about u-boot.

Is this something I need in addition or is it already included in the latest package (rock-4c-plus-ubuntu-focal-server-arm64-20230201-1231-gpt), and/or is it something you need to update (via ssh cli for example).

I know with the Armbian distro in their armbian-config utility there is an option to upgrade the bootloader but I have not come across any mention of similar in the wiki.

In the Radxa wiki, under development section, there are two links about u-boot

But here the first link just explains how to build and the 2nd explains how to use PXE.

I spotted in the 2nd link the following “U-boot of ROCK Pi 4 supports PXE boot and it’s enabled by default” so maybe it could be inferred that it is already included.

As such, just thought to ask this beginners question to get it out the way.

I am looking at the Github repository:
Here it lists different rockpi4 packages, including packages for u-boot.

What is not clear to me is which u-boot package is relevant for a Rock 4 C+ board and which to use for a Rock 4 SE board.

EDIT: Furthermore that Github repository does not apply to Ubuntu-focal. What do we use in that case.

Any assistance greatly appreciated. Thanks.