I donot understand this sentence:

"dirs_exist_ok dictates whether to raise an exception in case dst or any 
missing parent directory already exists."

How can a "missing parent directory already exist"?

My understanding would be that an existing `dst` would be OK (and copied into) but missing parent directories are just the ones above `dst` that also don't exist. 

Until 3.7, missing parent directories were documented to be auto-created (`mkdir -p`-style) according to the documentation ("The destination directory, named by dst, must not already exist; it will be created as well as missing parent directories."). Was this feature really removed? If not, then this part was accidentally (?) dropped from documentation?

What am I missing? I think, the documentation should be amended to make that clear.

From the code, this arg is simply passed to os.mkdirs() here:
https://github.com/python/cpython/blob/e6e34e45222b9c7a63ba92386612acf768082ba0/Lib/shutil.py#L450

os.mkdir is documented here: https://docs.python.org/3/library/os.html#os.makedirs

and says just "If exist_ok is False (the default), an FileExistsError is raised if the target directory already exists."

So I agree that the sentence you highlighted can be improved.

Would you like to submit a patch?

I would like to submit a patch for this. This would be my first contribution :)

I am starting on a patch now.

I've created a PR: https://github.com/python/cpython/pull/26634

I forgot to put a news entry, but hopefully that's ok since this is a very small change.