This symptom occurred all of a sudden with Nmap 7.80 and Windows 10 version 1909 (OS build 18363.836), where nmap tries to query using interface “eth0” :
Starting Nmap 7.80 ( https://nmap.org ) at 2020-06-30 11:28 Eastern Daylight Time
dnet: Failed to open device eth0
It seems that latest Windows updates is involved in this issue. Download the same or newer Nmap version (if available) and re-install it again to fix the issue.