The developer is expressing their opinion on their instance using their software. The beauty of federation and the software he has crrated is that you can build a community that you want.you never have to interact with or his instance.
It's a weird place to draw the line. You probably use all kinds of products with scumbag companies and owners yet you draw the line at a guy's Foss project which has nothing to do with his views and the project barely makes min wage yet serves tens of thousands of people.
You don't need to withdraw your support because you already do nothing to support. Again I think you are creating drama for the sake of drama. The guy is an open Communist and you are shocked that he's transphobic.