The function coloring problem represents multiple complaints. I disagree that the propagation of async makes the sync case irrelevant. In the frontend, receiving a promise has completely different implications on loading states. In the backend, I usually try to separate side-effects from pure functions, so the pure functions are usually sync.
Because JS is single threaded, fs.readSync will freeze the entire app. The only case where I would find that acceptable is in cli-scripts. But that could also be achieved with nodejs’ support for top-level await. There's perhaps a slight overhead from the Promise being created, but JS-Engines have so many optimizations that I don't even know if that matters. If nothing else is scheduled, awaiting a promise is functionally the same as blocking. Even in rare cases where you do want to block other scheduled events from running, you could achieve that with an explicit locking mechanism instead.
You could argue that filesystem access is fast so blocking everything is fine, but what if the file happens to be on a NAS somewhere?