What gives:
cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.5 LTS"
If it shows a newer version, probably you did a release upgrade being not supported.
If ok, you may try this.
I also see a RPi initramfs looking wrong here… Maybe you would reflash with a clean install.