My GRUB2 menu won't display properly, is glitchy, or blank.

Ensure that GRUB_TIMEOUT or GRUB_HIDDEN_TIMEOUT is present and uncommented in /etc/default/grub. Due to SeaBIOS limitations, at least on the Pixel 2, GRUB2 may only display in one particular resolution and color depth. Ensure that GRUB_GFXMODE=1280x850x16 is also set and uncommented.

An example configuration may be viewed here.

Don't forget to update your GRUB2 config as specified by your distribution.
Ubuntu: update-grub
Arch: grub-mkconfig -o /boot/grub/grub.cfg