For carplay and android auto, you'd plug your phone in via a lightening or a usb-c cable. I think there is wireless carplay and android auto too these days, but I'm not sure if that's available on many vehicles at the moment.

My Pixel has a headphone jack. It's the larger (3.5mm) of the two holes on top of the phone. However the poster is probably referring to USB or the wireless Carplay/Android Auto equivalents

Yes, Carplay and Android Auto either work over Bluetooth or a wire to the car's USB port.

Carplay requires actual wifi to be wireless, I'm pretty sure. It definitely doesn't work over Bluetooth! (You can of course pair your phone to your car with Bluetooth, but that's a different thing.)

Looks like it technically uses Bluetooth for connecting, but it does indeed require wi-fi for the actual carplay experience.

https://developer.apple.com/videos/play/wwdc2017/717/?time=4... (click 'transcript' then ctrl-f 'hardware requirements' for transcript)

Wrong. Pixel 4a does have the phone jack.