Off the top of my head I only know of one option to boot to a root TTY:
at the grub boot screen, select the Linux entry and press E for edit
then add a 1 to the end of the kernel command line
the line starting with “linux” and ending with “udev.log_priority=3”
add a space, then the number 1
then boot using F10 or CTRL-C (as is also mentioned at the bottom of the screen)
If you put a 3 instead of 1, you’ll get to your normal user login on a TTY.
Prefer that variant over the former
you’ll need to use sudo for admin stuff then, just as usual.