I'll say the electrical power grid. I can think of nothing else that separates modern life from ancient times in such a clear cut way and that the loss of would be insurmountable.
While antibiotics are a very important discovery in medicine, I believe the biggest reason medicine was able to develop like it has is the printing press.
At first I thought you were talking about dating lmao
Hmm I definitely agree that computers, and especially smartphones, are pretty damn amazing inventions.
But I agree with another poster when it comes to the greatest invention. When we invented the printing press, it allowed our species to develop much quicker because we were able to share information/education much better.
Electricity specifically generating/controlling it.
For the entirety of human existence and before humans even existed, electricity shaped our world and even kicked off the "spark" that allowed dna to propagate and exist from ~2billion years ago until today. But literally only ~200years ago, were we finally able to understand and create it.