Have there been any cases made public of officially designated terrorism incidents in which the people charged by USA (state or federal) justice officials either self-identified as Antifa or were described by the justice officials as endorsing Antifa ideology?
Short answer: if there were bona fide cases of Antifa terrorism, we would know about them already.
In fact, if there were, we would be sick of hearing about them by now.
Longer answer: The current president, Donald Trump, is in the reelection fight of his life. The Covid pandemic has been ravaging the US and stepping on his strongest case for reelection, the economy. The handling of the situation by Trump, his administration, and his allies has been, in the kindest non-delusional analysis, spotty:
Not only that, but a Woodward book revealed that Trump can't even plead ignorance of the direness of the situation as an excuse. And, as if to metaphorically encapsulate Trump's failure to protect the country from Covid, he failed to protect himself from Covid as well. As a result, Trump has been trailing his Democratic opponent, Joe Biden, in the polls consistently for months.
Actual cases of "Antifa terrorists" would be an immeasurable boon to Trump's bid for four more years
Needless to say, Trump is well aware of the desperate straits his reelection campaign is in, and has been desperate to change the subject from Covid for some time now. One way he has hoped to do so is by making the case that antifa are terrorists, who Joe Biden will "appease" if elected.
However, the tumult from the killing of George Floyd at the hands of police has mostly subsided, and for the moment, nothing appears likely to take its place. Some instances of the well-publicized unrest - ranging from peaceful protests, to looting and rioting - from that time might arguably fit some definitions of terrorism, although the definitions themselves are contentious. But insofar as the general public has any idea what "terrorism" is, it's something a lot closer to
"carefully coordinated and organized attacks that either target civilians directly, or cause indiscriminate collateral damage to civilians"
like McVeigh, Tsarnaev, bin Laden, Kaczynski, rather than
"spontaneous outbursts of public emotion that turn violent"
like basically all of the post-Floyd rioting and looting. In the absence of some indisputable public face--either a person or an organization--and indisputable public act of "antifa terrorism", and together with:
Trump's attempt to sell the country on the idea that "Joe Biden is weak on antifa domestic terrorists", or even that "fighting antifa terrorism [rather than ending the Covid pandemic] is the election-defining issue of 2020", has failed to take hold as it might have.
But if the FBI were to publicly announce an investigation into acts of antifa terrorism, and charge a specific perpetrator or perpetrators in court for their actions, all of Trump's messaging difficulties about Biden and "antifa terrorism" would--like a miracle--disappear.
Chris Wray, the FBI Director, is under immense pressure to produce an "October surprise"
Needless to say, under the circumstances, Trump has been strongly leaning on the FBI and DOJ to corroborate his apocalyptic visions of far-left extremists burning American cities to the ground. William Barr, Trump's Attorney General and the head of the DOJ, has mostly been happy to help. But Barr is (correctly) perceived as a partisan henchman whose main qualification for his job, from the beginning, was finding sophisticated-sounding ways to justify whatever insulation from legal or political consequence Trump and his allies require. As such, his imprimatur is not enough to move the needle of public opinion.
Chris Wray is another story. Although a Republican, he's not a firebreathing partisan like Barr, and therefore has the institutional credibility to legitimize the "antifa terrorist" narrative in a way Barr never could. But while Wray has confirmed that there are antifa-associated extremists that the FBI is keeping tabs on, his failure to follow Barr's lead and denounce antifa as Public Enemy No. 1 when given the opportunity has put him in the doghouse with Trump, who is reportedly considering firing Wray if he wins reelection. Under the circumstances, if Wray had the merest bone to throw Trump regarding antifa terrorist prosecutions, he almost certainly would have done so. And the idea that significant and undeniable antifa terrorist acts could have escaped the notice of both the FBI and the Trump campaign--much less that somehow a "deep state" in the FBI could have successfully hidden the conclusive evidence of antifa's terrorist activity from a Trump administration eager to exploit it and a 24-hour news cycle eager for more eyeballs and clicks--doesn't pass the straight face test.
So in conclusion: if the FBI had legit antifa terrorists to charge and prosecute for legit antifa terrorist acts, it would for sure be prosecuting them right now, and Trump would be tweeting about it every six minutes. The fact that this is not happening is strong evidence that they don't exist.