Actually is pretty easy and not different than older servers. Feature wise practically the only thing you lose is the ability to run dcpromo, but not the ability to act as a domain controller
Windows Update just gave me this KB, without me doing anything at all. Correct, nothing shows in Catalog
It is IP according to WSUS which generally mirrors WU. It comes under a special category "Windows Insider Pre-Release" as Windows 2022 does not have a category assigned yet. This category is generally assigned to the "Release Candidate" builds, which for some Windows 10 versions get upgraded to RTM eventually. This could be a good indication that 20348 is RTM in fact and this is something that we already believe. Note: Windows 2022 might eventually get the category of "Server, version 21H2 or later" as this is what shows under already assigned categories for drivers, but not for the OS itself. The older servers are designated as Windows Server 2016 or Windows Server 2019. The current Windows 10 versions are designated as "Windows 10, version 1903 and later", while Windows 10 defines anything up to and including 1809 (non-LTSB). LTSB have their category and the common updates fall under multiple categories, LTSB and non-LTSB.
When i get updates offered on WU without enrolling into any IP channel i consider them publicly released.
This is the reason why I say it is "Release Candidate". The same behaviour was previously with Windows 10 21H1 for LCU 2021-04 KB5001330. To make it more clear, to me 20348 is already RTM, only that it is not officially designated as release and as such it cannot be used officially for production purpose in Enterprise, unless on a special program and with Microsoft agreement of supportability.
MSFT tends to do their "no it's not the real thing, it's insider" till they officially announce it being officially released (same build, bumped delta build) for a while now, 20348 = 2022 LTSC, according to the publications i read and linked at at the OP
As you can see, I tend to make the distinction between what is under official support and what is not. For most people here and personal use supposedly for testing, it is RTM.
IMO is sure that 20348 will not change anymore, RTM will be 20348.xxx, we don't know what xxx will be I think that MS changed slightly is versioning approach relying more on minor rather than major version numbers since 19H1, which all in all is a good thing.