@feditips My blogs use Wordpress and I've always used the Shariff plug-in to generate the share buttons I choose, including Mastodon.

The first time you use the button, it asks for your instance and then, presumably, stores it in a cookie.

Sharing to Masto is always going to be problematic because Masto isn't monolithic so the button has no idea where to send the user without asking for more information.