How to prevent windows from automatically hiding offscreen after a period of inactivity

As per below - remove the addition Desktop by closing them

Add spaces and switch between them

The Spaces bar at the top of the Mission Control window contains thumbnails of each desktop space and each window that is in full screen or Split View.

To add a space, move your pointer to the Spaces bar, then click the add button  on the right:

When you have multiple spaces, you can switch between them by clicking the thumbnails the top of the Mission Control window. Or use these methods, which work even when you're not in Mission Control:

• Swipe left or right with three or four fingers on your trackpad, or swipe left or right with two fingers on your Magic Mouse.
• Press Control–Right Arrow or Control–Left Arrow on your keyboard.

Sounds like Hot Corners have been activated, but I am not sure as you mention a time delay.

Open System Preferences> Mission Control> Hot Corners

Have you activated Hot Corners, if so you can click on each corner and select the -

so they are no longer active.

Use Mission Control on your Mac