> ProcessPoolExecutor does not properly spin down and spin up new processes.

It is because Process "Pool" is for reusing processes.
If you don't want to reuse process, you can use the Process.
https://docs.python.org/3/library/multiprocessing.html#the-process-class

Or you can create ProcessPoolExecutor before starting bunch of jobs and shutdown it after complete the jobs.


> ProcessPoolExecutor also spins up too many processes and ignores the max_workers argument.  An example is my setting max_workers=10,
[snip]
> Instead, ProcessPoolExecutor spawns all 10 max_workers

What "ignores the max_workers argument" means?

And would you create a simple reproducible example?

Old ThreadPoolExecutor had the behavior (#24882).  But ProcessPoolExecutor starts worker processes on demand from old.