That's on me for confusing you with the original commentor who suggested adding PCIe onto that chip.
Also, Efinix hasn't proven themselves yet. I've been following their titanium line for years. Every year they say they're getting transceivers. And every part that comes out that was supposed to (first the Ti180, now the 375) is missing transceivers. Sidetracking here that I honestly don't know what's wrong with them, they've taped out a handful of these parts since I started using them, but they evidently cannot get high speed serial working.
Please don't put words in my mouth.
I see what you are saying, but you have to put my whole comment together. I am not saying that 8 bit MCUs are going to get GB/s capable PCIe.
Look at things like https://www.efinixinc.com/products-titanium.html with PCIe Gen4 on a 40nm SMIC process. Or more apt, the https://www.wch-ic.com/products/CH384.html PCIe to printer port bridge.
Arguing that I think an Atmega328p should be running PCIe is a ridiculous straw man.