The truth is that the actual stuff that makes browsers interoperable is downright boring. It's so boring. It's stuff like "this website broke because it was queuing requestAnimationFrame and setTimeout callbacks and measuring the duration between the two, and browsers were subtly different in their timings."
No browser vendors talk about this, because it would put you to sleep. Instead they talk about "standards," which are often niche, wonk-y features that no website is actually using.