Does anyone know how to deal with a patient with dementia smearing their feces while they sleep?

Lealonnie has a practical solution to your issue. I’m so sorry that you are struggling with this. You must be exhausted dealing with this challenge.

Wishing you all the best.

Change them on a regular schedule.

Yes; get the patient an Alzheimer's anti-strip jumpsuit that cannot be removed:

https://www.amazon.com/s?k=alzheimers+anti+strip+jumpsuit&ref=nb_sb_noss