POA abusing his power; what can I do?

My mother has early stage dementia. She is not real bad at all. She maybe won't be able to tell you what she had for lunch or maybe she will tell you something twice. Or for example: One minute she remembers the name of name of the corona virus the next she calls it something similar and says what's it called again? But she will remember always of the issue with the virus. Knows we need to find a vaccine. Knows the president. She knows where she is and what is going on. Understands and acknowledges she is forgetful. But other than that she is running around involved in activities at her assisted living facility. She washes her own clothes, bathes herself, gets ready herself, picks her own meals, takes her own meds. So pretty independent so to speak. She does not have oxygen or walkers or anything of that nature. Overall in good shape she just can be a bit forgetful at times.

Her brother is her POA. He has put her in an assisted living facility for 4 years. She does not want to be there. Never has. He has always told her don't worry you will get out. This isn't forever. He has been forcing her to stay there and to pay that and on top of that he has let her house just sit there for 4 years. So she is paying for an empty house and for an assisted living. He tells her when she gets better she can leave. Who are we kidding?? Dementia does not get better. It only gets worse so enjoy your years while you are still mostly with it! He has sold her dream after dream. I offered for her to come move in with me. He said no way because he hates me and doesn't believe I am smart enough for that. She really wants to but he has her under the impression she is stuck there and she has no say so in anything because he is in control and she needs to be there. He wants her there because it is easy for HIM. He wants to travel and not have to worry about her. He calls her maybe twice a week. He does not truly care for her emotions. She says she is just miserable. She always says to him I don't want to be here. I don't want to die here. I want to get out. He says "Well you have to die somewhere" He is just emotionless for her. He is throwing her items out which she never gave the okay to do. He told her he'd put him in storage because he will "get her an apartment" (That's just one of the dreams he sells her) She has asked to go to her own house just to see it.. he does not allow her to. He is not doing what is in her best interest or acknowledging her feelings. She lives miserable everyday. Yet, she is not exactly clear on what he is doing because he brainwashes her. He uses her weaknesses to his advantage. He keeps selling her dream after dream. I asked him to his face if he has any real intention on getting her out. He said no. Not until she is better. I told her to exercise to help her brain she won't do that. Like are you kidding me? You're going to punish her when she has her daughters house she want to and can go to?

I feel he is not actually working in her best interest but rather in what is easiest for him. As well as retaliation because he hates me. He is a control freak. He went as far as trying to stop her communication with me. As well as with her friend. He filed a police report against the friend of hers who has been there for her for years. He made he say what he wanted and now the friend can't visit her because he made a police report. The report is all in his words. Even says it is him vs the friend. Yet he made the living place stop him for visiting and told her there is a restraining order and she can't talk to him or she will get in trouble with the police. it was an incident report.. No restraining order! & She can do whatever she wants. Now that she has had time away from him in lockdown she is talking to the friend again as the brainwashing and scare tactics are not around her currently. She cries to me on the phone how she wants to get out of there and prays he has a change of heart.

My questions are.. what can I do??