Folder/file permissions & ownership looks good (same on mine).
But above 403 & 404 errors not.
This could be a misconfigured lighttpd.
Did you make any changes to the lighttpd config files ?
Or did you install other software that might have ?
pi@noads:~ $ man dpkg
-P, --purge package...|-a|--pending
Purge an installed or already removed package. This
removes everything, including conffiles. If -a or
--pending is given instead of a package name, then all
packages unpacked or removed, but marked to be purged in
file /var/lib/dpkg/status, are purged.
Note: some configuration files might be unknown to dpkg
because they are created and handled separately through
the configuration scripts. In that case, dpkg won't
remove them by itself, but the package's postrm script
(which is called by dpkg), has to take care of their
removal during purge. Of course, this only applies to
files in system directories, not configuration files
written to individual users' home directories.
Purging of a package consists of the following steps:
1. Remove the package, if not already removed. See
--remove for detailed information about how this is
done.
2. Run postrm script.
To reset everything to original state and restore the lighttpd config files, try purge the lighttpd package only (not dependencies) with below one:
sudo dpkg -P lighttpd
And reinstall (including dependencies):
sudo apt install --reinstall lighttpd
Might need to run Pi-hole repair afterwards to configure lighttpd properly:
pihole -r