I had a lot of hair thinning as well, eyebrows too. It seems as though covid can mess with your endocrine system. My hormones were all jacked up and also became hypothyroid which can cause thinning hair and brows. Maybe go to an endocrinologist to check hormone levels. I’ve been taking thyroid hormone as well as estradiol, testosterone and progesterone for about a year and my hair is growing back pretty quickly.
Much luck to you!