Here is the v2 release notes: https://github.com/pallets/flask/blob/master/CHANGES.rst

"*Async is not inherently faster than sync code.* Async is beneficial when performing concurrent IO-bound tasks, but will probably not improve CPU-bound tasks."

So many thanks for puting that very explicitly in the doc !

Python 3 is now over 12 years old. That's a very long time. And having a merge request open for almost 2 years is also a very long time.