In the last couple of days, Windows Security has started throwing a threat warning for Opera Installer on Windows 10, version 20H2 (I've got the insider preview enabled & set to Beta Channel).
See the screenshots of detailed thread message from Windows Security attached.
Here's the message box text copy:
Opera installer 73.0.3827.0.0
Fatal error upon loading installer executable:
In line 273:The operation completed successfully., In line 304:The operation completed successfully., In line 273:The operation completed successfully., In line 308:The operation completed successfully., In line 178:The specified procedure could not be found.,