Some philosophers write opinion pieces on Substack, e.g., Joseph Heath, a political philosopher from the University of Toronto, routinely does so. Outside of Substack, you can create your own blog series where you talk about different philosophical topics you find meaningful. Here, you can have free range on how polemical you want your polemic to be.
Moreover, you can always submit to academic philosophy journals. Academic philosophy articles, for the most part, are essays where philosophers explain why their view is correct while others are incorrect. That being said, they are not written as polemics - they are professional essays where the author engages with the philosophical literature by charitably presenting opposing views, advances their own, and responds to potential objections or actual objections in the literature. In other words, anything but a polemic.
Hope this helps!