It's worse than you can imagine. These "bad" cables are so advanced now they look like proper stock cables you would buy from a company directly (like apple). You can only tell if they have been fucked with if you know what to look for, cut them up or have a x-ray machine.
I am really, REALLY, thinking about buying a xray machine.
Shit, now you have me wondering if some cable makers ship their cables wirh spying hardware and ate just harvesting our phone data when it is plugged in.
Some of the cables have wifi/bluetooth/etc radios in the plug space itself now. That's how small that tech is now. They can create a network when plugged in and depending on how your device is setup (or if there is some sort of zero-day) it can pop the device and steal anything it can find.
The world is full of terrors that most have never even tried to consider. This is stuff you can build/buy. Not even "government level" stuff.
As if I didn't make you paranoid already, here is another post. This is at least a year old. https://counterespionage.com/malicious-usb-cables/ Archive: https://archive.is/wip/t7uFo
If this is what (((they))) allow us to know about, imagine the shit they are keeping secret.