I wrote a simple plugin to add buttons to the toolbar on mobile for easy insertion of an emdash and a right arrow (characters I use often on laptop and miss having on mobile).
I don't think I will publish it since I don't think many people have a use for these specific symbols and I don't think it's easy to make it more adaptable (since the buttons would have no icons if you simply added all the characters you want in a list in the settings). But I thought if anyone is interested, it would be very easy to adapt to the specific characters (or even often used frases) you are missing on mobile and adding the plugin manually.