I don't think you should be quiet, it makes them feel like everyone is agreeing with them and makes everyone miserable. Time to introduce you to my favorite game to play with conservatives, Politics Judo!

So you hear them rant about a thing. Some dumbass talking point. Let's use gun control. It's pretty easy to know in advance what the talking points are since they never shut up and parrot the same problem and solution over and over. "Shouldn't take guns, it's a mental problem not a gun problem".

Things are basically boiled down to a problem and a solution. A lot of people try to convince people that the problem isn't what people think it is, and that's hard to do. Even if they are just misinformed, it feels like trying to dismiss their fears.

So what you do is you agree with the problem, then use lefty talking points as the solution.

"Oh yeah, gun violence is pretty bad! And I love the Constitution, we shouldn't mess with that!" (Use small words and also throw in some patriotism, makes them feel like you're on their side. You want to sound like a right wing media con artist) "so instead of taking guns away, we should instead start having more, free, mental health care in this country. Since it's a mental health problem and these people are crazy, that is the solution that makes the most sense!" (Don't try to get them to agree to your solution, just state it as the obvious one)

It becomes weaponized cognitive dissonance. Their brains fry because you said the things you should to agree with them, flagged yourself as an ally, but then said the thing they were told is the bad and shouldn't want.

If they try to argue with your solution, rinse and repeat to a different talking point. "Oh yeah it might cost more, and we shouldn't have to pay more for it, so we should get the rich people who are screwing average hard working Americans over by not paying taxes to do that. We should shut down tax loopholes and increase funding to the IRS so they can go after them instead of the little guy"

Always sound like you're agreeing with them, but giving solutions that they disagree with that seem to be off topic but are related.

Either they will get flustered and stop, or they will slip up and say something racist or sexist or something, and then you can have HR bust them. Document it and also see if you're in a single party consent state.