readme says
On Windows:
(from a command window running as Administrator)
/Applications/Autodesk/maya<Version>/Maya.app/Contents/bin/mayapy -m pip install pymel
The path listed is actually the Mac path.
It should be:
C:\Program Files\Autodesk\Maya<VersionNumber>\bin
Which I've confirmed on my Windows workstation.
You can also cross reference against the Maya docs here which mention the correct install path. https://help.autodesk.com/view/MAYAUL/2024/ENU/?guid=GUID-72A245EC-CDB4-46AB-BEE0-4BBBF9791627