Is it permissible to wipe over only a portion of the feet during ablution and suffice with that, knowing that there is a chronic disease in the toenails that prevents washing them and to avoid humidity, and based on the doctor's advice to avoid exposing the nails to water as much as possible?

Washing the feet, including the nails and toes, is an obligatory part of ablution (Wudu'), except in cases of genuine or constructive inability. If the illness can be treated and the feet can be dried after washing, then they must be washed. However, if treatment is not possible except by avoiding water, based on the opinion of a reliable doctor or personal experience, then it is not obligatory to wash the toes. In this case, it suffices to wash the rest of the foot and the other limbs of ablution, then perform Tayammum for the unwashed part of the feet. If it is impossible to wash the rest of the foot without water reaching the toes, then it is not obligatory to wash any part of the foot. It suffices to wash the rest of the limbs of ablution and perform Tayammum for the washing of the foot. The injured person and the sick person are obliged to wash whatever parts of their body they can and perform Tayammum for the remainder. It is permissible to resort to Tayammum if the illness causes disfigurement and water delays healing, with the emphasis that resorting to Tayammum is only permissible when there is real harm from using water.