I think you need to lean on that point of connection. That the system isn't working.
I know it's difficult, but this is your own mother. All the people advising you cut her off or sneer at her every time she "starts", don't have a personal relationship with her. The only way to bring her back from the edge of going full conspiracy theory, is not to back her into a corner where it becomes a point of pride not to ever change her mind. You need to do the opposite. Keep the door open. And that starts with making her feel heard.
She's fixated on this because she's frustrated by the current state of the country and scared for the future. And she's not wrong to feel like that. Instead of challenging her at every turn, and making her feel judged, try to keep things neutral. Validate the basic concerns she has, but stay quite calm and indifferent to anything really out there she might come out with.
"I'm not sure about that", "I've heard a few different perspectives on that, I'm still working out what I think about it". That's how you want to be. Not telling her she's stupid or pushing her into any strong emotional reaction. And not patronising her like she's a child, because she will pick up on that. You want to create a space where she can explore ideas, but she can also change her mind. If you play it right, she might drop some of the more fringe conspiracies of her own accord.
If you can find voices who are a bit more nuanced and calm in their delivery, maybe steer her to them, and away from shock jock, algorithm-chasing content. And try to get her into something else, if you can. A lot of this is probably boredom. Does she have any hobbies she's let fall by the wayside a bit? You want to break her out of the fear loop she's stuck in and put some more positivity back in her life.