Measurements all pretty much match the Mac's Ookla results at 300. That app works fine on both the 12 Max and the 12 Mini. But two iPhones doing the exact same thing? So I dwonloaded a competing speedtest app which I do not usually like as much as Ookla. Had I only bought the one iPhone I would likely have put on my mask and gone to the Apple Store. I take care to match the chosen server to the one the Mac is using and it is an incredible difference. Sometime measures under 100, usually around 150. But when I run the app on both my new iPhone 12s I get the exact same results of very low speeds shown. It shows my Mbps speed to be at or even over the 300 Mbps line I pay for. The Ookla app on my iMac (2019) works great. But both show a disappointing incompatibility with the Ookla Speedtest app. A few days ago we upgraded to my iPhone 12 Pro Max and she loves her new iPhone 12 Mini. And it worked fine on my wife's iPhone 8 and on my iPhone 11 ProMax. I have used it on iPhones for years and years.

Net speed test by ookla