Is it permissible to straighten a thick, coarse, and tangled beard with an electric hair straightener (kāwiyah kahrabāʾiyah) to facilitate styling and grooming it?

If using a hair straightener is for smoothing hair, making it easier to style, removing tangles and frizz, and it does not result in harm, then there is no objection to it. It may even be recommended, due to the Prophet's (peace and blessings be upon him) saying: "Whoever has hair, let him honor it."