My system just spent 6 hours downloading the 1903 Windows 10 update and then my system ran slow afterwards.
I remembered that slowness was a problem with a previous update which was solved by disabling the unconnected Ethernet controller on my motherboard. Looked at Settings and found that it was “enabled” so I “disabled” it and the system is back to normal speed again !!!
You would think that Microsoft would keep a list of previous problem solutions and make sure they never happen again.
take care. Dale Kloss