I have the same issue with freezing (or apologising on repeat even when it's not my fault), especially in situations where I'm tired, low on spoons or (annoyingly!) in the workplace. However as far as I'm concerned, once someone is communicating with you by yelling, that's their problem, not yours. They're the ones who have caused the communications channels to break down & they're being abusive.

My advice is to explain that you're walking away from the situation & do exactly that (similar to a customer service rep hanging up on an abusive caller). You may need to develop & practice your explainer until you've got it flowing smoothly so you can just deliver it even with your mind frozen. If you can't deliver it in that state, don't worry, just walk away.
Keep your explainer short, a sentence or two at most (e.g. I'm walking away now as you're yelling at me. Please calm yourself down if you want to talk to me again.). Do not attempt to engage them further & keep away from them until they've got control over themselves.
Then make sure you get somewhere safe with other people around as social protection if the person yelling tries to follow you or escalate.

My best advice is to avoid people who yell at you. You can express your boundaries and let whoever know how that makes you feel, and what you can’t accept.

If the yelling isn’t retaliatory from some bad thing you did to them, you could also ask them if they are okay.

Fight, flight, freeze, fawn. Your brain chooses freeze.

I don't know if practice (being yelled at?) would help or entering situations knowing you'll be yelled at or what.

Silly question: does freezing cause you problems? I could see it defusing the hypothetical situation a bit, I could also see it making the situation worse.

Same. Total shut down when someone raises their voice or gets otherwise hostile to me. Though it can quickly turn into a meltdown if they keep pushing, and I'm much more afraid of that and hurting someone. Though it's not like people being that hostile toward me is super common, I still worry about it.

You can't, that's why manipulators are using it.