did you try with this \\yournextcloud@SSL\DavWWWRoot\remote.php\dav\files\username
It works for me for windows 7 to 10 and server 2012, but be aware that it sucks, it’s slow and don’t work with Microsoft Office files.
You have to use mountainduck (not free) i didn’t found a good one free.
It should be good if it’s just for backup