Climate change, same sex marriage (though, perhaps not as shocking as some might expect, ditto anything trans related), potential mars colonization, coming off the heels of the Spanish flu, COVID news would probably freak em out. Ooh, the USSR being gone, and China being a world super power. The USSR would have been new to them, and it collapsing less than a century later would probably feel quite odd, especially if you could make them understand just how incredibly advanced the USSR got in such a short amount of time. Tons of stuff.
In the 1920s a state fresh off a recent regime change disappearing would have been extremely par for the course. You telling that to someone from the 1960s would probably have more of an effect.
I mean, if you showed them a map it'd look nothing like their current political divide. I'm not sure they'd be more shocked by the state of what then was Soviet Russia than by Czechoslovakia being broken up or the other half a dozen changes in Europe alone.
I’m Czech, and exactly 105 years ago (October 30, 1918) the approximately dozen nationally aware Slovaks met in an inn and wrote a letter to Prague that they agree to be part of Czechoslovakia as the “Czechoslovak nation” because they knew they couldn't form a state on their own, and split off the hated Hungary. The 4 people who signed our “Declaration of Independence” 2 days prior needed someone to represent Slovakia so they went in the streets searching for a Slovak. Vavro Šrobár, a nationally Slovak lawyer who incidentally just arrived to Prague, came forth and signes the document, and became Minister of Slovakia a few weeks later.
The Republic helped Slovakia reach its industrial potential and gave its people democratic values (except for WWII, we don't talk about Slovakia in WWII). Eventually, Slovak politicians wanted power so they broke off after true democracy was restored in 1989. The Velvet Divorce was so uneventful compared to the end of Communism that people did not really care at all.
So I agree that to informed people in 1923, Slovakia being separate a century later would be no surprise. However, the formation of USSR (which I know much less about) was pretty controversial and involved a civil war so they might be actually be surprised it did last 80 years.
On the other hand, the other changes you glossed over are quite significant, especially with Germany and Poland.
Show them a time lapse animation of the countries borders as they changed in real time such that a second equals one month. Two minutes of "what the fuck just happened‽‽"