You can draw straight lines by line command. (Shortcut: L)
It looks like a line command in profile command.
For using; Click the left mouse button to select the first point of the line. Then click LMB to select the endpoint of the line.
I rarely use line command. I prefer to use the profile command for drawing straight lines. Because in profile command drew line endpoint becomes the first point of the next line. But in the “Line” command you draw every line by selecting the start and the endpoint.