Nobody is trying to stop Elon Musk from buying Twitter except for Elon Musk himself.

Twitter, the banks lending him money, and the other investors Elon lined up are all trying to make the transaction go forward.

So the answer is clearly that yes, Elon musk is "allowed" to buy Twitter if he actually wants to. He may even have to buy it based on the agreement he signed even if he no longer wants to.