Please use the existing thread.
Yes. Will be fixed in Whonix 13:
https://phabricator.whonix.org/T144#7370
Error starting VM: operation failed: device matching mac address 00:16:3e:5e:6c:0d already exist
Note:- happened even before with non-whonix templates. i dont think it is specifically related to whonix.
Answered here: Error starting VM: operation failed: device matching mac address 00:16:3e:5e:6c: - #3 by Patrick