I can feel your frustration and burnout. You are definitely not alone. Dementia care is a long term fight, it will be nice to have "a support team". From your text, I can't tell if any social resource can be utilized.
Are there any associations such as Alzheimer Association around you offer caregiver support? Go join a caregiver group (physical or online), you might learn different care approaches from other family caregivers, places are friendly to dementia patients, or tricks to transfer the attention and so on.
Do take good care of yourself, it's actually the top priority.