I use Proton Drive as my cloud storage provider. In Windows Explorer, I have a Right Click Menu option of 'Always Keep on This Device' when right clicking on any file that has been backed up to Proton Drive. This Right Click Menu option doesn't appear when Right clicking a backed up file in Opus. I have no idea whether this an Opus problem or a Proton Drive problem. Maybe someone with more knowledge of things could advise?
If it's of any help to anyone, this is the web page for Proton Drive Syncing:
I am not sure, in that case, unless it appears if you hold Shift while right-clicking.
These days most of the context menu handlers that don't appear in Opus are like that because they are checking the process's name and including/excluding different processes for some reason. Although it's also possible the issue is something else.