Hi there Kevin,
Hope you are well.
I am running a 2015 Chromebook Pixel LS and I'm wondering if you could possibly help me as I'm at my whits end :-)
I have enabled developer mode and legacy boot/usb boot using the commands readily available on Google but whenever I try to boot from any USB stick (I've tried USB 2 and 3), The screen just corrupts and the machine appears to hang.
I know its running SeaBios as it tells me after I have pressed CTRL+L and it then offers me a boot menu with my devices correctly listed but its after that where the corruption starts.
Completely by fluke on one of my linux usb sticks, I removed it and reinserted it while the corruption was on screen and that did actually allow the boot but obviously this isnt good for my USB integrity.
I do hope you can help, I found your email via a google search as someone else seems to have had the same issue but there where no fix instructions that I could find.
Finally, I've tried to see if its possible to update/re-install seaBios but there's nothing i can see online for beginners such as me.
Thanks for your time.