Dementia wife believes I'm having an affair, nothing I say or do helps, she just gets angrier and wants a divorce and has changed house lock.

Time now to either call EMS for transport to the ER and then to contact SS to get the needed assessment and evaluations, even if it requires a 5150 hold.
If EMS will not transport wife with you and your daughter there explaining the problems then you will need the assistance of APS (Adult Protective Services).

I would attend an attorney with your daughter at your side, as well. You are going to need to have division of finances when your wife is placed in care, which is almost certainly a necessity at this point. She requires more than you can provide for her as one person who is not young, yourself, anymore. Social Services, in the hospital, is going to need to be aware also, that placement is going to have to occur now.

Wishing you good luck and hope you'll update us.

She cannot legally change the locks unless her name is the only one on the deed. Will the police assign you a social worker? At this point in time, it's good that the police/authorities have been notified of what is going on, but it may be time to call in for a mobile crisis unit to come and do an emergency psych eval. I can't remember the exact name, unfortunately, but you can search for your state's crisis services hotline. I'm so sorry you're going through this.

Run off to Hawaii with your “imaginary” friend? I dunno. Since you have done everything you can do, maybe you should go along with it. Stay at a hotel a couple of towns away and stay out of touch until the inevitable happens.

After you get the call, rush to the ER and insist on a psych evaluation. Don’t bring her home because you can no longer take care of her with these issues.

I’m sorry this is happening, but it appears that the marriage is over, and you don’t deserve her abuse.