Curious- Picking audio option when you’re using TV’s speakers

[Mayboy128]

I was watching Sleeping Beauty on my little TV. It often can be difficult to hear the dialogue, and definitely the music lyrics, on old Disney stuff. I switched from the default 7.1 to the 4.0 option, and noticed that it was quieter. I don’t have any external speakers or a soundbar.

This made me wonder:
What happens when one selects different audio options, if one doesn’t have additional speakers? It seems to put all the sounds into the TV’s built-in speakers, but sometimes I will notice differences in volume and perhaps mixing.