The unresponsive Space Bar key during the boot is still puzzling. It is also an annoyance as it prevents entering Safe Mode and its diagnostic capabilities.
Whenever you have the time, it would be great if you could:
Try with a different keyboard (borrowing a friend’s keyboard)? to assess if the issue resides within your current keyboard.
If the same issue is observed with a different keyboard, then it resides within the system - maybe the BIOS. A remote possibility is that the Space Bar key is intercepted by a software component loading ahead of the boot loader. The Space Bar key has a special meaning for Grub and Windows during their initial boot phase (from the code read with the MBR?).