When I press enter it generates a line that I cannot edit and after it the cursor is placed. In the markdown it is seen that there is an empty line, which I can eliminate and the text looks normal, but with it it looks very separated taking away important space.
Try using shift + enter instead. If you are using the the Rich text editor and then switching to the markdown editor, that is a current limitation that you have to use shift + enter to do a line break instead of a new paragraph
No method to reverse the functionality of the two Enter commands currently exists. It’s been asked about many times, but has never been implemented, neither officially nor in a plugin.
It’s worth noting that the new Rich text editor for mobile has resolved the issue of needing to use shift + enter to do a single new line. The eventual plan is this editor would replace the Rich text editor on desktop so that the code is common between desktop and mobile, but there would need to be feature parity between both editors before doing so, and there is no estimate how long this would take to be implemented.