I was using this shortcode to create a keyboard shortcut, for copying the public dropbox link of a file:
ContextMenu ITEMMODE LABEL "Copy Dropbox link"
After updating to the latest version, it stopped working.
Can't reproduce on my system. Tried successfully with Dropbox 143.4.4161 and Opus 12.26.3.
But Dropbox has been a bit flaky in the past weeks and wanted to be restarted on several occasions for no apparent reason. So maybe try with a fresh Dropbox installation before you dig any deeper.
Try selecting the file and running ContextMenu SHOWCMDS, then use the UI that opens to create the command for the menu. Does it give a different command to the one you're using now?
(With the file selected, you can run the command by typing a > and then typing/pasting the command into the lister. No need to create a toolbar button for it, unless you plan to use it a lot.)
Are you holding Shift when you right-click the file? Run ContextMenu SHOWCMDS SHIFT if that's the case.
Otherwise, it's possible DropBox have changed the way their context menu works in an update, such that it's no longer possible to run it programmatically via the normal method.
If you're on Windows 11, DropBox may have done that because of Microsoft's decision to introduce a new type of context menu handler in Windows 11 and relegate things that don't use it to a sub-menu in File Explorer. Which would also explain why it still works for people on Windows 10 (where the new type of context menu isn't needed, and wouldn't work, and so wouldn't be installed by DropBox).
Check it hasn't been added to Preferences / Miscellaneous / Advanced [Troubleshooting]: ignore_context_menus due to instability.
Other than that, there's nothing that would happen on the Opus side which would make a menu stop appearing 2 days after an update if no configuration has changed and you haven't gone to or from elevating dopus.exe when you launch it. Something on the dropbox side is more likely.