It may allow you to boot again in the normal Windows system. Start by going into the BIOS settings and find the 'Reset to factory defaults' entry. That doesn't sound as something you can recover from without doing a full re-install of Windows 10. The aborted firmware update (I doubt it was actually system-bios, probably firmware for sound-card or network card) might actually have added a (temporary) 3rd boot entry to the startup that you prevented from running to completion, but that is still acting as the default boot. With a broken dual-boot setup, partially applied Windows Updates and possible BIOS/EFI settings that don't match with the installed Windows version(s). So you managed to really mess up your system. Here's a screenshot of the prompt at the start of the laptop: (NOTE: This is a picture from the ASUS website, I'm not sure whether on my laptop it said 'Easy Flash utility will allow.'

Is the update written on my SSD or on the BIOS itself? Will formatting/resetting my Windows 10 remove the scheduled update of BIOS? I suppose it can be completely bricked with the update? Also, in Device Manager, there’s “System Firmware” entry with the exclamation mark inside a yellow triangle under Firmware. I suppose that I’ll get the Yes/No option again if I restart/turn off and turn on my laptop again. Now there’s a “Restart required (Your PC needs to be restarted to finish setting up this device: System Firmware)” notification in the Windows notification area. I chose No and the system booted into Windows again. Then at the very beginning it said something like “BIOS will be updated in 60 seconds” and there was Yes/No option. It asked for restart, and I restarted the laptop. Then restarted laptop, and decided to update the ASUSTeK Firmware also. I’ve updated my Windows 10 with Windows Update, then went to optional updates, and updated the drivers there also (there was an ASUSTeK Firmware update, which made me suspicious and I left it off).

Update bios asus windows 10