@penfold welcome to the forum.
As @CalebJohn says, if you are using the Markdown editor to create your notes, rather than use the WYSIWYG editor to see your notes, it's probably better to use the Markdown editor's viewer pane. You can then see your Markdown and how it renders at the same time. The pane is activated using (1) in the picture below. What this button shows can be controlled using options that can be set at (2). The picture below has Joplin in "Split View".
Joplin will accept asterisks to create bullets and they remain as asterisks if you use the viewer pane and not WYSIWYG (3).
Markdown itself does not allow multiple blank lines when rendered. So you may put multiple blank lines in the editor (4 & 5) but when the Markdown is interpreted no lines are shown if the blank lines are at the start of the note (6) or one line if it is between text (7).
However using the Markdown editor and viewer pane (rather than switching to WYSIWYG) does mean that you will not lose those extra lines in the editor.
Please ignore the fact that my copy of Joplin may look a bit different from yours - missing buttons, different text sizes and colours, added note tabs - my copy has been customised