When you paste in a Latex Formula, for Example: $${x, y)^{} x{x, y}^{}$$ it should automatically recognize it as latex.
Also I think it would be nicer if you could just write latex formulas without the orange field appearing and instead that you just type $$ to start and end a formula and once you are done editing the specific rem it renders the formula. But that you sill see a preview when typing underneath the rem.
You can paste text enclosed with $$ and it will be parsed as LaTeX, e.g.
$$x^2$$
There must be something else wrong on your end. 
Sometimes Ctrl + Shift + V does something.
Your example above does not render correctly because it has mismatched braces: {x, y )
I created a small plugin that transforms rems that have latex written in them enclosed by one dollar sign $ to latex.
For example if you have the following rem:
this can be transformed to latex: $a^2$ which might be useful if you copy over latex formulas from snipping tools like Mathpix and to create cloze (mark the formula before converting)
And you call the plugin with a shortcut or /pluginName the plugin looks for $ and changes the markdown of the current rem which is selected, so that the latex gets rendered.
If you wan to check it out you can just add the website as a plugin. Use at your own risk.