how to get rid of multiple desktops in big sur

I've been using Macs since 1987, and somehow I have never encountered the multiple desktop feature until today, Feb. 5, 2021.

How do I get rid of it? All of the answers to this question I found on this site were posted 4, 5, 6, or more years ago, and none of the solutions seem applicable to Big Sur.

I discovered it by trying to switch between files in the same application and finding I could not do it without switching desktops, which I didn't even know was a thing. I just hate this feature and want to get rid of it. How?