Stuck on Monterey update - Intel MacBook Air won't go to Safe Mode, NVRAM reset doesn't seem to work, no startup keyboard shortcuts work

A non-tech savvy friend updated his Intel MacBook Air to Monterey, got it stuck in an update error, and gave it to me to try and fix it.

I tried to reset it using all the startup keyboard shortcuts I could find (Safe Mode, Option, Command+R, Shift, Command+P+R, Option+Command+P+R, holding the power button for 30 seconds)... nothing changed. I couldn't get to any of those. The keyboard is working - if I try to Command+Q in the Update Assistant, it asks me if I'm sure about quitting.

The MacBook always starts on the black screen with the Apple logo and a white bar loading, with the countdown "About XX minutes remaining...". After it "finishes," it goes to the MacOS Update Assistant screen, with the message "An error occurred applying the software update."

When clicking "OK" on that, it asks me to "Choose Startup Disk" and to "Select the system you want to start up your computer". However, no option is offered, with the only clickable button being "Target Disk Mode" underneath it.

Since I don't have a Thunderbolt cable nor another Mac to transfer the data from this one, what else can I do to recover it?

Any help would be greatly appreciated.