That can come from a vitamin B deficiency. Best products are similar to those for chapped lips,
Mineral oil
Petrolatum
Shea butter
Sun-protective ingredients, such as titanium oxide or zinc oxide
White petroleum jelly
It also helps to use products that are fragrance free and hypoallergenic.
Also I’d report the symptom to your medical team to hear their recommendations. I’d also avoid salty or spicy food that irritates. Hope healing comes soon! ☺️

Also if you have sores in your mouth the doctor has stuff for that

Chap stick works fine for me