Try selecting Don't replace Explorer, then click OK, wait a few seconds, then go back in and select the recommended setting and click OK again. That should re-write the relevant registry settings, in case they're damaged. (Note: It can take Explorer a minute or so to respond to the change, and it may continue to use the old settings before it has.)
If it still does not work, make sure Opus is not set to run as administrator and also not set to run in compatibility mode.
If it's still not working after that, please run FileTypeDiag and click Save without typing an extension, to export the folder registry settings to a text file, and attach the results for us to look at.