There are A LOT of integration products now available on the market for these reasons. Pac, Metra, Navtv, etc. Makes it plug and play with no cutting/splicing required in most cases. Most intercept the signals from the head unit and send super clean and flat signals to whatever aftermarket stuff you want.
Sad to witness this cottage industry (as with many others; like VHS rentals @Blockbusters) shriveling up and going away.
I must have owned about 14 new cars, 13 of them had their 'radio' systems de-gutted and upgraded to sound instead like 'audio' systems.
In the fourteenth one (2-Din head-unit on a '06 Goat), was so well integrated into the rest of the vehicle's electronics (including steering-wheel controls and funky amps hidden in weird places, etc.) that I decided to leave its 'radio' system as much OEM as possible (except; by adding an Aux input patch to the head-unit PCB).
The integration of the automotive audio-systems have become so complex and so well integrated w/i the vehicle electronics that even the simple task of swapping power-amps is near impossible for vehicles made in the 2020s!
RIP!