This is the first upgrade I have done since I started with RPi. Going from the latest stretch to buster on a 3b+. Tried 2 different times following different tutorials. 1 used "apt full-upgrade" and the other used "apt dist-upgrade". Both completed without errors and I verified the kernel and OS had been upgraded. However, when I rebooted, it went to the command line instead of the GUI. I tried changing the boot options and resolutions with raspi-config but nothing has worked. The version of stretch I upgraded was a full version with GUI. Although I usually run this machine headless, I used an HDMI monitor and dedicated keyboard/mouse for the upgrade.
Just as a test, I installed a fresh copy of buster and all is fine so I know it's not a HW configuration issue.
Any help will be greatly appreciated.