This is a new change to 24H2 clean installs, it's following an "upgrade" process even though it knows a clean install is happening. You will always get an empty Windows.old folder, even if you wiped the disk. A different setup client is running which does the work. If you're running a manual install, Setup will eventually offer you an on-screen link to revert to the old-style setup.exe.
MS has offered no explanation or guidance on why it needs to be different. You will also get a mandatory Windows Update screen at the end of OOBE, to force update your Windows before you're allowed to logon.d
Well, I have just tested it on a clean install on a 24H2 VHDX I clean installed to a few days ago. I had to use the previous installer on
3rd page of installer, as there is a bug using the ridiculous new installer installing to a vhdx file.
On very first page, I pressed shift+f10 to get to command, and ran diskpart, attached vhdx file and it had all windows files.
I then did a "clean all", and exited diskpart.
I carried on and installed to the vhdx file (all unallocated space), and clean installed 24h2 (creating local account with oobe\bypassnro method).
It worked perfectly and no sign of a windows.old folder.
As you say, this is probably an artifact of the new installer.
One irritating aspect also of the new installer is the new oobe update screen which forces the cumulative updates, as you say. This can take ages depending on internet and drive type (easily up to 30 minutes or more). This is a terrible move - previously we could oobe on version on usb drive, do the initial configurations, and then use WU to get cumulative updates.
Fortunately, we still have the previous installer. Even if MS stupidly remove option for old installer, there are at least two options:
1) use 23h2 installer replacing install.wim and boot.wim in sources folder with 24h2 versions.
2) use dism to install 24h2.
Make sure you feed back to MS how crap the new installer is!
