Could cataracts cause tiredness?

Sometimes. Cataracts interfere with vision making you work harder to see. This could increase the feeling of fatigue.
Potentially. Poor vision can cause depression, anxiety, tiredness; If have best glasses & tear film stable & still have decreased vision, glare (esp night driving), halos around lights, a cataract is likely present & surgery likely best option. Info: eyedoc2020.blogspot.com.
No. Cataracts reduce vision - but they should not cause tiredness. Please see your medical doctor to figure out the cause of the person's tiredness.