I can't agree more...
Long old story (have a look in the forum using the search)...
For example, read this:
"The newline error in the Joplin code - #9 by james-carroll"
A lot of us would like an option for that...
At this moment if you want to have only one line (and not two) press "[SHIFT] [ENTER]" instead of [ENTER] only.
WYSIWYG editor = RTE = Rich Text Editor