I agree with your larger overall point, but this specific part isn't true.
Nothing has changed recently, but green card holders/permanents residents (over the age of 18) have been required to carry their green card with them since a long time ago (since the implementation of the Alien Registration Act of 1940, according to Google). I remember back when I got mine in 2012, it was a requirement as well (though, I will admit, it was not really enforced).
Here is the relevant quote from Section 264(e) of the Immigration and Nationality Act (I.N.A.)[0] addressing this:
> Every alien, eighteen years of age and over, shall at all times carry with him and have in his personal possession any certificate of alien registration or alien registration receipt card issued to him pursuant to subsection (d). Any alien who fails to comply with the provisions of this subsection shall be guilty of a misdemeanor and shall upon conviction for each offense be fined not to exceed $100 or be imprisoned not more than thirty days, or both.
And here[1] is an additional resource confirming this.
0. https://uscode.house.gov/view.xhtml?req=granuleid%3AUSC-prel...
1. https://www.nolo.com/legal-encyclopedia/do-i-really-need-car...
That's terrible advice, please stop giving terrible advice like that. ICE need to have probable cause (about you specifically, by name, not just your street or zipcode or "people of your ethnicity/appearance" or "people in that store/restaurant/parking lot"), beyond a verbal "uhh we think you're here illegally". You have the right to ask them why. And the 4th Amdt still exists, for all people, so no they can't stop you in your vehicle or inside your own house without probable cause and a [signed, valid] warrant [naming you specifically, and signed by a judge].
> How are you going to prove you're a citizen?
If you're a citizen, you can simply state to them you're a citizen (better when you're on bodycam; and repeat it (on bodycam) to any other ICE officials you interact with, and make mental note of their names or else descriptions so you can subsequently identify them). Pragmatically, you could also identify yourself as such to any bystanders or anyone videoing things.
"U.S. citizens do not have to carry proof of citizenship if they are in the U.S." [0] Read that again and again. Ok?
For sure ICE could knowingly violate a citizen's rights, detain them unlawfully (for hours or days), beat them up, send them to a detention center, even (in very rare cases) deport them. That becomes a political as much as legal matter. If you have constitutional/legal rights and due-process but refuse to stand up for them, do those rights functionally cease to exist? Do they magically get restored in 2029(/2033)? Time to stop being complacent.
(Obviously noncitizens do not have all the above protections, and need to be more careful.)
In the meantime, to inform yourself about your rights, and to get advice how to deal with ICE, both for citizens, GC holders, visa holders, visitors and undocumented people, see: https://www.aclu.org/ or other webinars. But, stop speculating or spreading misinformation. If you don't know, ask here.
[0]: https://www.aclu.org/know-your-rights/immigrants-rights
This is technically true but in practice (as we've seen multiple times recently), if ICE wants to stop you or interrogate you or even arrest you, they will do so without a warrant.
So, you could conceivably be a citizen, but CBP/ICE think you might be here illegally, so they can stop you without a warrant. How are you going to prove you're a citizen? There is no national ID, passports aren't required nor are they held by the majority of citizens, and unless something has changed, green card holders / permanent residents aren't required to carry their papers.