Pressing the Ctrl key (alt / option key under macOS) when you click at each wall end while drawing 2 walls, it's pretty fast to draw a closed round space.
Yes, this is my fault. I set the coordinates from the wall properties edit menu. Zooming in, I saw a gap. By removing it with the mouse, I was able to create a circular room. True, in the figure it is displayed multifaceted, but in the general view it is round.