Can my brother, who is our mother's POA, have her put into a nursing home with hospice for 5 days, and have them withhold all of her meds?

Depends on the type of POA he has and if mom has been found to lack capacity.

Janiel, your profile and previous postings state that your mother died in January after your sister placed her in hospice care. I'm very sorry for your loss, which is still very recent and must still be very raw; but can I gently ask why you're now phrasing this question in this way?

The simple answers to it, though, are:

a person with medical power of attorney can - must, actually - make decisions for someone who is not able to make them for herself. That would include placing her in a nursing home, and agreeing to her admission to hospice.

a person with medical power of attorney must give consent to treatment, and equally so to withdrawal of treatment, for someone who is not able to give consent herself.

So, yes, these are standard POA duties.

I don't think you understand how Hospice works. Hospice is the end in most cases. Some people have lived longer than the 6 months, some have improved and been discharged from Hospice care. Its not unusual to have all "life sustaining" medications removed. There are some medications they don't remove because without them, it will cause discomfort and pain. Morphine is given for pain and to ease trouble breathing. Hospice is there to keep the client comfortable.

I suggest you call the Hospice Agency and ask if they can provide you with a grief counselor.

To answer ur question, yes your brother had the right as POA to put Mom on Hospice care.

Yes. The POA is appointed to carry out, for the person who appointed the POA, to the best of their ability the actions in the best interest of the person who conferred the POA to them (given that the person is no longer competent to act for him or herself.
This includes end of life care. If a physician has told the POA that there are likely fewer than six months of life left, and if the POA believes that the person would have preferred quality rather than quantity of life, then the POA can and SHOULD ask for hospice. A part of hospice is the elimination of drug meant to "treat" a person. Those drugs that are meant for "comfort" remain and are added. The POA also decides where the incompetent person, unable to act for him or herself, will live, including a nursing home.
The entry into hospice also eliminates all appointments and tests that were to CURE what cannot be cured, and that the is approach of death, expected within a half year's time.

Country Mouse says there's a profile, I see none now. Was it removed? I also see original post has been shut down from further comments. Which too me is weird since we have postings still open further back then 2019. I only see the one post from Janiel in 2019. Even though Worried mentions, in that post, a post where OP gives more info. And Country Mouse comments about other posts. The only one I see under "following" are from other people. Am I missing something?