Is it permissible to publish religious posts on social media, even though the one calling to Islam is not a scholar, and bearing in mind that calling to Allah on such pages may be restricted to scholars?

There is no harm in publishing for the sake of da‘wah (calling to Allah) via the internet and social media, provided that what is published is verified as authentic, taken from well-known scholars, and adheres to the Sharia guidelines. It is a legitimate means for da‘wah.