You can in most cases press the HTML button in Tinymce toolbar and add (copied) latex there
The main problem in writing latex in editor mode is that the first space given by your keyboard is usually unicode character "space" (U+0020) - the same character that you get with html entity   or   - but Tinymce is using a workaround for adding several spaces in queue and it converts the following spaces (after the first space) to nonbreaking spaces ( ) even if you don't see the difference in editor content area. And Latex syntax can ignore normal spaces but it does not understand what nonbreaking spaces are and shows odd characters...
The other possible way to get whitespaces to your editor mode is to copy latex examples from some web pages and there can be for example line breaks etc in the visible code - or bold, italics, red, font size 16px,...any css tags that are used to make the code look more pleasant and you may need to copy the examples first to some simple texteditor (notepad) or use the Paste as plain text-plugin. Still it does not always work since many unicode characters can look like "normal spaces" or they may be invisible whitespaces like in that previous (last) example.
Most math plugins strip some unicode spaces but do not try to strip all possible whitespaces.
As you can see it is possible to add whitespaces directly in Dragmath - and dragmath is always used in editor mode