I had the same issue. My root cause was that I forgot to update:
from stretch to buster
sudo apt update
reported an additional ~ 200 packages that could be upgraded.
sudo apt full-upgrade
completed without error, but alas, still no X server, still no display found in the Xorg.0.log.
But I was now able to install xserver-xorg-video-fbturbo
(It doesn't currently auto-upgrade because it's still marked "testing" in the repository as of 2019-10-12)
I also ran raspi-config to make sure auto-logon to the desktop was enabled (yes, I know, that's a bad idea!)
Check the contents of this file:
ExecStart=-/sbin/agetty --autologin pi --noclear %I $TERM
Mine was missing
pi and was causing my auth.log and syslog to fill up with agetty complaints.
xorg.conf? Have you tried removing it?