My (24F) mom (51F) treats everything as transactional and acts entitled.

For some background context I am the main person who cooks in my house. I mainly cook for myself because I am very particular and eat really healthy, my mom rarely ever cooks so many nights I will offer her food because she’s my mom, but there are many times where I meal prep for the week because I’m in grad school and need to feed myself. Many times I make healthy sweet treats for myself as well and she will go in the fridge and eat things without asking. Usually I will ask her if she ate said food, and then say like hey I would appreciate if you would ask before eating my stuff like I made that for myself it is upsetting. It has really reached a point where I am sick and tired of going to grab things and either my mom or my brother (23M) has eaten it without asking. ( she also treats my brother the complete opposite of me) As soon as I try and talk to my mom about these things she throws everything she does in my face. For example today I asked her if she ate one of my brownies and she said she was having a sugar craving, I told her that she is not entitled to everything I make and that I told her she could have one and emphasized ONLY one. She continues say “It’s expensive for the protein powder and creatine, and i don’t ask you for money. I went to (pet sitting client) for you and didn’t ask for money. I’ve bought cat food several times when you were away. I think eating a brownie shouldn’t be a big deal” which I think is completely transactional dismissive and wrong and so I said that and she comes back saying “All relationships are transactional. you do for each other without expecting something in return, But people should do stuff in return” but then she is basically saying she is doing all this stuff without asking for anything in return but then completely expecting stuff in return. And when I say she was acting entitled she tells me that I’m an entitled child who expects her to do everything for me, mind you I do all my own cooking (for myself and her), laundry, dishes, cleaning, she pays my phone bill, feeds the cats, and cleans the litter boxes and her own chores the way I do. I don’t want to transactionalize it myself but it’s just context, I certainly don’t expect her to do ANYTHING for me knowing she acts this way whenever I need a favor. I really don’t know how to deal with her because I can’t move out yet, I’m starting my second masters in the fall and every time I start school and become more busy she gets way worse and tries making my life harder when I’m already busy as it is. I’m getting my masters to become a therapist and no matter how hard I try to talk to her in a healthy productive way she just pushes me to react (I know I’m responsible for my reactions) I just don’t know how to get through to her that not everything that is mine is just automatically for her too. But I guess the bigger issue is that she is very invalidating and selfish about everything this is just one situation. One moment we are friends and doing fine and talking, the next she does something and I have to tell her it upsets me and she turns every situation around on me, makes it transactional, and then says something hurtful and usually not true. Does anyone have any advice or similar experience with a parent?

TL:DR, my mom is very transactional and acts entitled to everything I cook or make and whenever I have an issue with anything she does she acts like a toddler that didn’t get her way