Does Joplin have a "live preview mode" that allows you to work and edit inside the preview pane, without needing the edit pane?
Try rich text editor (right icon in the bar above the editor)
If not your cup of tea, give rich markdown plugin a try
This is interesting and kinda cool, but not exactly what I am looking.
Ideally I'd like to type markdown, but as soon as I move to a new line, the previous line hides the markdown and line is just rendered.
As mentioned above the Rich Markdown Plugin is the closest you can get to that experience in Joplin: Plugin: Rich Markdown
It is possible to do this with the rich markdown plugin by adding css to hide the markdown code on non-selected lines. I did this for a while and it was nice. However at the time (don't know if it has been resolved) there could be a problem with cursor placement into a line that revealed it's markdown after the placement.
I did a work around for a while where I just made the markdown "invisible" but it still took up space. But eventually I just gave it up and live with the markdown visible.
BTW, there have been many posts about this topic. Might want to search a bit to get more info.
There's always the option to set your external editor - I actually love using Mark Text... it's an issue TBH mostly that Joplin doesn't save or manage folders in the same way - I'd love to make documents in Obsidian or Mark Text and have them appear (as with Obsidian) in the editor - but also sync to Joplin on my ipad.