How do you know when it's time for palliative care?

Give him what he likes , sprinkle little sweetener on it honey or sugar to give that sweet taste. Try applesauce, puddling , thrive even Ensure, Boost . He stopped talking because no one to converse with . Brain shutting down . Get a friend of his over to spend couple of hours . Talking

He may recognize you by face only might give you another name. That's ok .
He might be depressed of his condition. Why me ? He doesn't wish to be like this. So he's giving life up

C
.( The saying is don't use it you loose it . )
Is his limbs good, chair exercises in the morning (Television) or video for seniors. Do what he can , need to get up movement.

Respectfully

It’s so sad isn’t it! I’m watching Mom doing the same. She’s 85 in June.

You call the PCP to get a consult for palliative but it sounds like you need hospice. The consultant will tell you if your friend qualifies. Your friend or HPOA might need to give consent

beccalevin: Now is the time for palliative care OR perhaps hospice.

It sounds like your friend is actually ready for hospice care and not palliative care as the 2 are very different. Palliative care is the step before one goes under hospice care, and if your friend isn't eating, and losing weight, that should qualify him for hospice.
However, you being just a friend have absolutely no say in this situation, unless of course you are his medical POA.
Hopefully he has a family member that is his POA, who can get hospice on board sooner than later.

Now. Now is the time for hospice if the doctor feels your friend has 6 months or less to live.

Best of luck with a difficult situation.

Do you have POA?

If you are not POA, as a friend, none of this is in your control.

A person with dementia needs someone caring for him as either POA or guardian. The decision as to palliative care falls them to the POA/guardian and the advance directive or wishes of the patient himself.