Boot logging to file in ESP

Can U-Boot log its output to file?

I'm a digital nomad operating a RPi 4B headless. I have 2 boot USB keys: one "known-good", and one for experimentation.

Plugging into a monitor (which I don't have in my backpack) isn't trivial.

Is there a way to have U-Boot write all output to a file on the ESP so I can read it from there rather than from a monitor?

Thanks, Tom