Can't delete a Section

I don’t know what setting has gotten messed up, but suddenly Delete doesn’t work like it always has. I selected a section and pressed Delete. Instead of removing that section, it deleted just the audio in that section, leaving a gap that looks like a lighter shade of gray on the screen.

Does anyone know what I screwed up? It was working normally 5 minutes ago. I’m running Audacity 2.4.2 on a Windows 10 PC.

Tracks > Sync-Lock Tracks can sometimes cause seemingly confusing behavior, but I am not sure that this matches your description.

“Edit menu > Preferences > Track Behaviours”
You may want “Editing a clip can move other clips” to be selected / enabled.