I don't think anyone's tried to push mRNA vaccines for polio yet, and if they did it would be a really obvious swindle - they'd run right into the same problems with the vaccines not being sterilizing that we already did with Covid and with the existing, well-tested inactivated polio vaccines that almost everyone in the developed world already has. In principle it's more or less the same problem even (inadequate mucosal immune response, though in different mucosa...) They'd just be harder to manufacture, ship, and give to people than the existing inactivated vaccines, when those are already the main problems stopping the existing ones being deployed more widely around the world.
