My rabbit won't stop bullying my cat

I have two bonded rabbits. A male and female. Both are fixed. I recently adopted a cat off the street and she is fixed now too. The rabbits free roam in the living area of my apartment while my cat's territory is my bedroom. I even put up a gate to keep my rabbits from going in my bedroom. That being said, whenever my cat does venture into the living room by jumping over the gate, my male rabbit relentlessly chases her, runs into her and bite her if he can reach. She can't go anywhere without being followed by him. My cat may hiss or hit if provoked but she generally leaves the rabbits alone. It's created such a stressful environment. I wish he would stop being so territorial, it's like a game for him! Any advice?

I'm not sure if there is a way to stop that behaviour, maybe giving him treats in his food bowl when the cat comes in the room to distract him? I trained my rabbits with treats to come running when called, they stop doing whatever they do and I can even call them up to introduce dogs to rabbits. Creating a connection between the cat and something yummy in the food bowl would be something I would try.

Since afaik even just scratches from cats can pose a danger to rabbits, and there already is trouble brewing, I would do my best to keep them seperate when you are not in control of the situation. Like, with a full height gate at that door.

We use child gates as a barrier and have put 2 together so it is 6 feet high--none gets over. Your bunny will never change the behavior, so you will need a better barricade.

Right now your rabbit sees your cat as a threat or an invader in his territory, and is trying to chase her off. He doesn't understand that the cat is now part of the 'rabbit warren' of your household. So you need to try and change that perception. And that could possibly be attempted in the same way you begin the bonding process with rabbits.

Put items with your cats scent in your rabbits area so they get used to it. And having them in pens next to each other to get used to one another's presence isn't something that can be done for this situation, but you could have feeding times near each other, with a baby gate or xpen to keep them safely separated initially. Then eventually you may be able to remove this barrier, but still strictly supervised. Though for this stage I would try it in a room your rabbit doesn't see as his territory, so he's likely to be less territorial. Kind of like how you would use neutral territory when bonding rabbits.

https://rabbit.org/behavior/cats-and-rabbits/

It's all about exposure and positive reinforcement. Your rabbit needs enough safe time around your cat to see her as part of the heirarchy in the household. But be aware that any changes you make to your rabbits environment or routine, runs the risk of starting territorial pooping and peeing, and could also cause referred aggression to occur with your bonded pair.

Whatever you do try, remember that extreme caution is needed when cats are around rabbits. One nip or scratch from your cat, could result in a fatal infection. And there's also the potential exposure to toxoplasmosis. So just be aware of those risks and take the necessary precautions.

https://wabbitwiki.com/wiki/Relationships_with_rabbits