What does the ending of "The Favourite" mean?

The ending is sort of symbolic and up for interpretation. My interpretation of it was after Queen Anne had her stroke and dealing with the effects of it she is now living in misery.

She is sort of alone having only Abigail left who the Queen is somewhat realizing is frivolous and cruel. She had banished Sarah (Rachel Weisz's character) whom she clearly felt a bond with so her mood is further dampened cause of that. And to add suffering a stroke on top of all that it has only left her feeling alone and miserable.

The montage of rabbits consumes the screen, each rabbit a reminder of each of the Queen's deceased children she lost in childbirth. The misery consumes the screen and the life of the queen and those that try to curry her favor. Abigail's face is pained and sad as she has to bow and bend to the Queen's whims. I think that is what the montage of rabbits is supposed to represent but that is up to interpretation I think.

According to Collider:

The Favourite‘s ending makes itself very clear. All three women are now stuck in their own personal hell.

Abigail, who escaped her horrible marriage and a life of sexual submission is now slave to another master. “My life is like a maze I continually think I’ve gotten out of only to find another corner right in front of me,” Abigail tells her miserable new husband mid-way through the film. By the end, she may no longer be laying among the sickly and she won’t have to watch unwanted men jerk off at her, but her life of luxuries is dependent on the queen’s favor and she remains trapped in submission; still locked in her maze of sexual servitude.

Sarah’s fate similarly leave her trapped in her nightmare. The woman who cared about queen and country above all else, is exiled from both. Sarah was willing to sacrifice her husband to the war if it was the necessary price, she loved her queen very literally for most of their lives, and now she is banished from her life there. Her hell is in her absence.

As for the queen, her health is rapidly degenerating and she is more or less helpless without Sarah’s stern missives to follow. “She saved me my whole life, without her I am nothing,” the queen says when Sarah first goes missing, and there is truth in it. Sarah was strict, but always with love. She would not let the queen have sugar, lest it hurt her stomach. Left to her own devices, Anne binges on blue cake, throwing up between bites. Left in Aibigail’s care, the queen asks what would happen if she fell asleep in her mud bath and slipped under. “Imagine it’s hot chocolate,” Abigail says. To be with Abigail is to drown and choke on your indulgences. Without Sarah to care for her, Anne really and truly is left with no one who loves her, just her rabbits — the stand-ins for her true happiness — and the very manifestation of her trauma and grief take over the screen until they multiply and are all that remain.