writing this answer with the hope that it will help folks in 2023.
GRUB_CMDLINE_LINUX="fbconsole=rotate:1"
is what works on the kernel command line.
As an Archlinux user running kernel 6.1.6 and latest version of grub, i can confirm that the above command line also ensures that all virtual terminals are rotated clockwise.
For the record, 'rotate_all' is not recognized on the kernel command line.