Go to > System Settings > Menu Bar. Do you see the Drop Box toggle there to turn it on..
If your menu bar is full, the items on the left of the menu bar will automatically be hidden when that space is needed. You can disable some items at the Setting location above until the Drop Box item appears in the Menu Bar, then Command-Click on the Drop Box item and move it farther to the right so it is not one of the menu bar items that are hidden when it gets full.
If your Screen Resolution is set to make the display bigger for larger text, there will also be less space in the menu bar to display items.
If you use the third party app Bartender to also manage the Menu Bar, that app had a bug where it was not working correctly and could cause problems with the Menu Bar. You can check for an update to that app or remove and test to see if Drop Box shows up again.