Nypenthe’s Work-around did not work for me. However, disabling Discord’s overlay did work. Game is running in windowed mode.
To disable Discord Overlay, In discord, bottom corner is your name, along with a gear icon. Click the gear icon, then select overlay from the left hand side. At the top you should see the option slider to enable and disable the overlay.
Hopefully that will work for others as well.
Blizzard Post by Aggrend is what helped me. His post / response can be found here https://us.forums.blizzard.com/en/wow/t/classic-crashes-when-enabling-vsync/245855