So I decided to come back to all of this after a while and try out the latest updates. But right after I enter the update password and click "Yes" the device just boots into recovery mode.

I've tried leaving it therre for a few minutes but nothing happens. There's no way to control the recovery menu (it says to use volume up/down and power buttons, but I guess it doesn't mean the MMI buttons.) Turning the car off and on again, the device does boot back up normally, but there is no update happening.

I've tried downloading the file again, tried using an otherwise empty SD card, tried renaming Update.zip to update.zip, tried removing and reinserting the card while in the recovery menu, pretty much everything I can think of. Am I missing some intermediate updates, maybe?

This message pops up very briefly before the recovery menu shows: