I haven’t had time to update my family member’s FP4 yet, sorry, but you can follow these instructions to get it:
If you are extracting the image after the update but before you rebooted, make sure to get the other slot you aren’t currently in. If you are already running the updated system you’ll want your current slot.
If you lost root, get the previous boot.img
from the kernel page, patch that and fastboot boot
it. You will get some error messages if you are on a different version, but it will do for extracting the boot.img
you need.
Have fun