Unable to update [Core v6.0.4 FTL v6.0.2 Web interface v6.0.1]

I am trying to run pihole -up but I get the below error message. I can't get a debug token either. Before I updated to v6 I didn't need to run sudo. Is this part of the problem? Running "sudo apt update" doesn't work either.
Hardware is Pi 3B+ on current Raspberry Pi OS.
Everything seems to be working OK though, apart from this:

Debug Token:

xxx@raspberrypi:~ $ sudo pihole -up
[✓] Supported OS detected
[✗] Update local cache of available packages
Error: Unable to update package cache. Please try "sudo apt update"
xxx@raspberrypi:~ $ pihole -d
[✗] The Pi-hole command requires root privileges, try:
sudo pihole -d
xxx@raspberrypi:~ $ sudo pihole -d
/usr/local/bin/pihole: line 86: /opt/pihole/piholeDebug.sh: Bad message
xxx@raspberrypi:~ $

This look like an OS level issue.

What happens if you run sudo apt update?
Does it work? or do you see error messages?

xxx@raspberrypi:~ $ sudo apt update
Hit:1 http://deb.debian.org/debian bookworm InRelease
Hit:2 http://deb.debian.org/debian-security bookworm-security InRelease
Hit:3 http://deb.debian.org/debian bookworm-updates InRelease
Hit:4 http://archive.raspberrypi.com/debian bookworm InRelease
Reading package lists... Error!
E: Encountered a section with no Package: header
E: Problem with MergeList /var/lib/apt/lists/deb.debian.org_debian_dists_bookworm_main_binary-arm64_Packages
E: The package lists or status file could not be parsed or opened.
xxx@raspberrypi:~ $

That's indeed an OS level issue, not related to Pi-hole.

Did you perhaps run an in-place OS upgrade to bookworm recently?

What's the output of:

ls -lah /var/lib/apt/lists/

I don't think so! But after the last response I tried to fix the OS using something I found on google, and managed to brick it. So I just did a complete reinstall. All looks good now. Thank you!