On PopOs, I’ve set up /etc/modprobe.d/blacklist.conf with:
blacklist cros_ec_uart
blacklist cros-ec-uart
And set up it on the kernel:
kernelstub -a modprobe.blacklist=cros_ec_uart
This has completely disabled this problem for me. The C13 ain’t my main device, but I don’t have boot problems with it anymore.