Just as a small input: The old protocol function has been removed by Mastodon. So there is no way, like with the other services, to just have a simple share link. You first have to create a form for the user to enter their instance and then create the share link based on that input. Nothing complex, but in order to avoid a horrible user experience you still will need a couple of hours to find and design the best way that fits with the rest. It’s certainly on my list, but currently between family, job(s) and other activities there is not much time to focus on this. If anyone wants to take a shot at it, the Github repo is here: https://github.com/3UU/wordpress-shariff-wrapper (Just please follow the WordPress Coding Standards closely).
Of course the best solution, in my opinion, would be something like diaspora* has provided: https://share.diasporafoundation.org/?title=diaspora*%20Advanced%20Sharer&url=https://share.diasporafoundation.org/
Maybe someone can develop the same for Mastodon. Would be much cleaner than having all share button plugins for all CMS out there develop their own solution.
Cheers
JP