Saying Apple “can’t” put a backdoor into their own devices is an absolute claim, they’re the ones who control the software, so it’s possible in principle. Business incentives and bug bounties reduce the risks sure, but they don’t eliminate the pressure or legal mechanisms major governments can apply. Snowden’s documents showed that governments have methods to compel or exploit access, and implementation flaws or covert agreements can defeat cryptography in practice.

I do have a solid foundation in how these systems work. You should read the GNU Manifesto and learn about Free Software, it explains why blind confidence in a completely proprietary stack is to remain untrusted. No one should ever be this certain a proprietary system will always respect users rights.