Because UpdateAgent.dll do most of the work i just tried, it also works without SSU (you must add the SSU separately first)
MSU is just a cab file with different extension Place cabarc.exe next to the folder that contain cab files then run from cmd inside the folder Code: ..\cabarc -m MSZIP -r -p N ..\22000.msu *.*
No, it's only available (and updated) with each UUP build DesktopDeployment_x86.cab however, only available within msu files (because no Windows 11 x86 released) it's used if the Host OS is x86
Eh the cumulative would be rolled into the December update though I guess the cumulative for December might be a bit smaller and focused towards security more than bug fixes. Not sure about January but perhaps things have resumed fully in time for when that monthly update schedule is due. Core improvements and larger fixes will probably land once the build for Windows 11 H1 2022 is I guess on the beta ring and starting to turn into a release build in time for well, no idea when it's planned April or May perhaps if it's still going by a roughly six month schedule. And then all over again for the fixes and stuff that remains on dev until the H2 2022 build. EDIT: Would be nice with a more detailed changelog for these updates as well but at least the support page has some details though nowhere near what the insider blog had for .282 but that's just a small observation. It's that update with the signature fixes and what else and there's .318 and the servicing stack component.
The normal monthly LCU and whatever at patchtuesday is released, will be available, only the preview/optional non security updates won't.
Funny that the file naming still goes "windows10.0-kbxxx" instead of something like "windows11.0-kbxxx".