I would like to let you know that balenaEtcher v1.5.77 was just released, and includes a fix for this issue.
Thanks for your report and let us know in case you still face the issue while using the newer version.
Also about the error being show, it only shows the writer process failing and no error message users can follow up with (except for contacting dev support)
Unfortunately, at the moment, there isn’t much we can do to make Windows Defender trust etcher. Your best option is to turn “controlled folder access” off