To be fair, didn't his dad figure out most of the new element and Tony just put the clues together and finished the work? And JARVIS was explicitly made by an accident that he couldn't figure out how to replicate and JARVIS helped make Ultron (which he based on the internal structure of the Mind Stone), though FRIDAY, EDITH, and Betty are all pretty impressive on their own.
That said, Tony's most impressive feat was probably figuring out Time Travel by himself in an insanely short timeframe after merely learning that tech that allows travel into the Quantum Realm exists, without even trying to actually get access to said tech in order to do so first. That said, the tech needed to get to the Quantum Realm was the product of Hank Pym's entire life's work, and Tony couldn't even replicate the Pym Particles needed for the process in that short timeframe (though apparently Thanos had the tech needed to replicate and mass produce enough Pym Particles to transport his entire army across time and dimensions in relatively short order as well, which leads to the horrifying possibility of Thanos with a Giant Man level boost to his strength).