Linux secure boot was a little weird last I checked. The kernel and modules don’t need to be secure boot signed. Most distros can use shim to pass secure boot and then take over the secure boot process.
There are dkms kernel modules that are user compiled. These are signed using a machine owner key. So the machine owner could for sure compile their own malicious version and still be in a secure boot context.
Yeah. The suggestion I saw was that instead of retracting the gear they mistakenly retracted the flaps.
Now in the video the wings do look quite flat. But yes, it would be hard to say for sure in a video of that quality at that distance.
The descent looks (to my untrained flight sim eyes) to be controlled albeit without power.
At 400ft agl they had very little options most likely. Not even much choice in what they hit.
Very sad all round.