It seems like it’s still possible to disable Gatekeeper on macOS 15: https://discussions.apple.com/thread/255759797
I haven’t tried it though. It’s so rare that I want to run something unsigned, I prefer leaving it enabled and then allowing whatever it is I want to run.
There’s a headphone jack on the other side. I don’t think Apple make a computer without a headphone jack. Most models have more than two USB-C ports as well and all current models have a dedicated “Magsafe” charging port.