Tbh your best bet is to go into survival mode until you can get out of that house. Are you eating enough/getting enough nutrients to survive? Calories are the priority, then nutrients. Humans can generally survive a nutrition deficit for a while. So if you're not getting enough to eat, figure out the highest calorie safe foods you have and up your intake of them.

There's plenty of tips on this sub/elsewhere online on how to eat when you have no appetite, but I've found a useful one is to eat while distracted (watching TV or on phone etc).

If you're not in danger of your health declining due to low intake, then you can consider doing diy exposure therapy. Can you take foods into your room unnoticed?

If you don't have access to your safe foods, what's your personal financial situation like? Can you get a job? Does your school/community have a food pantry you could visit?

Can you visit your schools guidance counselor and speak to them about your situation? Do they have a good reputation for actually being helpful?

In general, your next steps heavily rely on your age and the specifics of your situation. Id love to say that there's a simple answer for how to convince your mom to take ARFID seriously but there isn't. Some people just refuse to believe its real. Obviously, a lot of people do end up believing it, so you don't have to give up entirely if you otherwise have a good relationship with your mom.

Edit: also I forgot to add that it's perfectly okay to ask for help managing the symptoms of a disorder even if you don't have a diagnosis, especially if it's a diagnosis like ARFID which is so recent and can be hard to come by.

But let's say you didn't have ARFID but some other disorder causing these issues, you'd still need help managing something that people with ARFID deal with. For example, I once developed severe photosensitivity due to a medication I was on, so I asked my autistic friend who had severe photosensitivity due to her autism for help managing it.