If you want to know what actual high security development looks like you can just look to Orange Book Level A1 certified systems and Common Criteria EAL 6/7 certified systems. Systems designed for high security with formal specifications, robust documentation, exhaustive testing, thorough review, spotless penetration testing by well-funded intelligence agencies, formal proofs of correctness, and proven deployment in high criticality settings. The Common Criteria SKPP literally required the NSA to fail a multi-month penetration test while having the full source code, internal documentation, and formal specification.
These commercial vendors believe protecting against state actors is literally impossible even though it has already been demonstrated in front of their faces for decades. Nothing they say about security is useful because they know nothing about what is needed to make systems that are actually secure.