Mere software difference

How else should it be implemented?

NFC. We have NFC tags embedded in single use tickets for travel and events, the cost is marginal and most of the uses relevant to card readers could reuse cards.

Add a physical shutter to cover the camera when it is not in use. (In addition to avoiding spying, such a cover can also sometimes avoid the camera being dirty that it would not work when you are trying to scan something.)

That's an extra moving part that will break, get jammed, or will trap dirt/particles between the cover and lens and effectively sand off the lens over time.

The solution is proper, enforced anti-spyware and anti-stalking legislation (so not the GDPR), not hardware band-aids that are trivially bypassed.

The real solution is a better software culture that looks like GNU/FOSS. Such a culture would generate laws like that if a problem persisted but likely wouldn't need them.

The solution is cash.