The poorly-named 'FRAMEBUFFER' option in initramfs-tools controls whether the console_setup and plymouth scripts are included and used in the initramfs. These are required for any initramfs which will be prompting for user input: console_setup because without it the user's configured keymap will not be set up, and plymouth because you are not guaranteed to have working video output in the initramfs without it (e.g. some nvidia+UEFI configurations with the default GRUB behavior).
The zfs initramfs script may need to prompt the user for passphrases for encrypted zfs datasets, and we don't know definitively whether this is the case or not at the time the initramfs is constructed (and it's difficult to dynamically populate initramfs config variables anyway), therefore the zfs-initramfs package should just set FRAMEBUFFER=yes in a conf snippet the same way that the cryptsetup-initramfs package does (/usr/share/initramfs-tools/conf-hooks.d/cryptsetup).
Should it set KEYMAP=y too, like cryptsetup does?
I've created a PR upstream and done some light testing:
https:/
Are you able to confirm that this fixes the issue wherever you were seeing it?