How do cheap Raspberry CSI-2 cables get around differential impedance matching
CSI-2 interface data pairs require a 100 ohm differential impedance.
The flat flex cable used with Raspberry Pi CSI-2 camera interface has 0.5mm pitch.
A cheap unshielded laminated polyester FPC cable with 0.5mm pitch has about 100 ohm differential impedance in the configuration where a differential data pair wires are between ground wires.
So basically, they don't work around it. The cable pitch is simply chosen so that it has a geometry that has a differential impedance that is very close to the required impedance.
This will vary somewhat due to the differences in geometry, manufacturer and materials, so the matching is not perfect by all means, but it is a surprisingly accurate match.