First of all, quantity is a quality all on its own. This has to be repeated often, having one of something is far easier then having 1000s. So even if, nothing in Starlink was knew, nothing that is one Starlink was ever produced the way it is for Starlink. Starlinks vertical integration and mass production is totally knew in the sat industry.
Now since you might not want to count that (despite mass production of sats being a huge challange), lets look at some other things. While Electric propulsion isn't knew, it wasn't exactly common specially for non science missions. Starlink v1 used Krypton, as far as I know Krypton wasn't used on operational sats. The Starlink v2 Argon thruster is pretty damn revolutionary in its performance and the first use of argon on operational. So if you want to name 'one' thing this would be it and it isn't really debatable.
Starlinks laser communication is top of the line in terms of performance and having a whole constellation of laser link sats coordinating for best connection is certainty unique. And not as a research project, but actually operational on commercial sats.
Starlink flat construction is also pretty unique, making so many sats stack-able is a significant advance if you compare it how the other largest constellations were deployed. There is additional innovation in the way they are deployed threw a rocket rotation and a spring mechanism, its unique and brilliant.
The Starlink sats also use a sun shield to make the sats harder to see for earth observation, as far as I know this has not been done before.
Starlink operations is also whole unique, on a personal per sat bases SpaceX is leading by far. SpaceX has a very small team for operations and made excellent use of automatic avoidance on a large scale, doing avoidance even for even unlikely collisions.
We simple don't have all the information, we don't know everything there is to know about the antennas for example. They are likely quite a unique design as the ground terminals are, but we just don't know.
I could go on to talk about ground systems as well, be lets leave it here.
The simple reality is, Starlink as system is fundamentally revolutionary. Any claim that cheaper rockets is the only 'new thing' is basically putting a board before your head and screaming 'lalalalal'. Even being charitable and assume that all individual technologies were demonstrated as research before doesn't change how revolutionary the system as a whole is.