Look up telogen effluvium. Any big change can cause temporary hair loss. So a change in diet, giving birth, death of a loved one, divorce, illness (covid!) can do it. Usually it occurs a month or two after the change when the hair having entered its resting stage early then falls out early. When the next growth cycle is due it usually restarts. Most of us find it it only lasts a few months and then you begin to see the new baby hairs regrowing. Coincidentally many people have panicked and bought all sorts of supplements in the meantime and credit that not time for the return to normal.
obviously also check that things like iron and thyroid are ok though.