Hoping this might help someone else having the same problem. Yesterday (19 Oct 2020), Windows 10 updated on my PC. The apparent result in Vegas 18 was that the headers "File, Edit, View, Insert, etc." at the top of Vegas were all blacked out. Only a black rectangle appeared where those headers should have been. My first thought was, what could have changed since the day before, when everything was working properly. I check my Windows updates, removed the 2 updates (one was a system update, the other a security update), rebooted, and all is well again. Whew! Right in the middle of a project, too.

My graphic card is an AMD Radeon, which was my first suspect, as the driver for that was also recently updated. But undoing the Windows update solved the problem for me.