1) grub REALLY does not like a receipt printer at COM1
2) i have yet to learn if it’s possible to let the kernel think tty1 doesn’t exist, while redirecting the keyboard to ttyS0 input, and let ttyS0 output to be printed onto the receipt printer. do not send information on this topic, i want to sleep.

how do i even explain to lucifer when i die that, the reason i committed grave environmental sins and have like 6 meters of receipt paper with GRUB instructions on them is that GRUB sends the whole line to the serial port and the receipt printer would print the whole line despite a one character update

@kuriko 'note that GRUB assumes that your terminal emulator is compatible with VT100 by default. This is true for most terminal emulators nowadays, but you should pass the option --dumb to the command if your terminal emulator is not VT100-compatible or implements few VT100 escape sequences' - worth a try?