After a certain update that struck a while ago it is no longer possible to browse EFI partitions, mounted with mountvol in explorer under Windows 10.
The same goes for Opus, whenever you're trying to access the mounted partition with or without administrator access it comes up with "The system cannot find the path specified".
However, it is possible to use explorer++ to access the partition as described here: https://www.insanelymac.com/forum/topic/311820-guide-mount-and-access-efi-partition-on-windows-10/
Would it be possible to add EFI partition support to Opus?
Explorer++ is not doing anything special here. The key thing is running the process as admin, presumably because the mountvol tool isn't mounting the drive properly for the standard user (at least if mountvol is run as admin as well). Running Opus (or Explorer) as admin will let you access the drive in the same way that Explorer++ can access it.
Be aware that Running Opus (or Explorer) as admin will cause problems, since the rest of the software running on the desktop can't talk to it and ask it to do things like open folders. Running as admin si not recommended (using the UAC support and built-in Admin Mode is almost always a better choice), but it can be done if really needed. We'd recommend only doing it temporarily, and re-launching as the normal user when finished whatever you're doing that requires access to the EFI partition.
You can use File > Exit Directory Opus to close down the Opus process. After that, you can re-launch Opus as admin in the usual way. Do the same thing when you want to return to normal.
The FAQs have a guide explaining some of the things that can go wrong when running Opus as admin, so you know what to look out for.
It would be way more convenient to be able to run a separate instance as admin in parallel instead of having to restart each time, but oh well...
Thanks.