Tutorials tell you to use "Tools -> Options" to get an options windows. These days you just click on the three lines in the upper right (sometimes called the "hamburger icon" to get a menu and select "Preferences". Make sure the "composition" pane is selected and the "general" part of that pane.
Near the bottom is a checkbox option labelled "When using paragraph format, the enter key creates a new paragraph". De-select this and there you are, .... except .....
This option has now been changed to the much more cryptic "Use Paragraph format instead of Body Text by default". There is probably nobody on the planet who knows what this actually means, but de-selecting it does still fix the problem of the enter key producing two blank lines, so go with turning this off.
What we really want to know is, what are those people smoking?
Adventures in computing / tom@mmto.arizona.edu