I was quoting the creator of the PR. In the MacOS thread he said:
It seems to be way better when exporting using the single-threaded export template.
Whether this is true or not should be obvious soon, because the PR listed in my post just got merged! 
There is still an issue with audio cackling on low FPS, but it’s a big step forward to making Godot viable to use on the web: Cracking audio with Godot 4 no-threads Web builds · Issue #87329 · godotengine/godot · GitHub