Login to SPO Site Using IE, Make sure keep me logged in is selected
Open IE -> Go to ‘Internet Options’
Select ‘Security’ tab -> Select ‘Internet’ Zone.
UnCheck the box for ‘Enable Protected Mode’
Make sure the ‘Web Client’ service is started on the client machine.
Open the SPO site -> go to the Document Library
Select ‘Open with Explorer’ [ Make sure this is working fine ] Copy the URL opened in explorer in the address bar
Delete IE Cache.
In IE ‘Trusted Sites’ zone add
Open Windows Explorer
Click On Map Network Drive
Paste the URL copied