Doesn't yubikey have an HID mode where it acts like a keyboard and types a static phrase? You could do something like that for boot. Or possibly more complicated. Idk if modern bootloaders support cooler modes where the key resides on the yubikey.
Edit: according to the arch wiki, there are quite a few potential options there if you have a yubikey. Wiki
Please tell me suyu is a deliberate play on "sue you."