For right-click, the current version of Windows' folder view, Tools|Folders Options, the /File Types\ tab, choose a file type and then the [Advanced] button gives you access to file associations for that, to edit in or out what you want. Or regedit and search for the rogue "Opens with XYZ Media Editor"/whatever to easily track down all of the image, video, sound, smell and taste files that this addition has been made to. (*Warning - messing with regedit is powerful, obviously.* Though if you look enough before you touch you should be able to understand the depth of the rabbit-hole that you actually need to go.)
Not file types. Stuff like "Add to Dropbox" or "Convert to PDF". 7-zip is great about letting you configure what's there, Dropbox and WinMerge let you disable it, but others aren't so nice.
CoveredBut you should also see things like "File Folder" under the File Types of the Folder Options, that covers non-files, and other weird stuff. I mostly use that to go and add an ampersand in, via the Advanced button (Edit File Type dialogue), to (re)specify a shortcut key of choice, yet you can go and delete them out that way, too.
Or track them down all ".../shell/Send to Dropbox/command" branches, or whatever, registry keys and prune out the. "Send to Dropbox" branch (leaving the "Open", and other "Send to..."s under Shell, unless you're
very sure that's something you also want to do). But look around before you do too much. Export to a file to read (open with notepad, or your notepad replacement of choice) a selection of HKCR/(stuff)/shell branches to get an idea. You can also go in and add the Ampersand in on the key, this way, if (like for me) this is the thing youbwant to do.
But this was never intended to replace a good Goole-gained reference to a much more considered page on how to do this properly. For one thing, they
may have changed things by the time of Windows 10. I doubt it (given backwards compatibility with most of the historic Win9x-and-up programs that have been designed to poke in their own menu items, user-authorised or otherwise) but if installer requests are intercepted by a given API (like the WOW64 abstraction layer does for other things) and converted, it may change without n ways that manual pokes would discover.
And some global menu items sit under places with different formats, but are equally discoverable by a search, like I did with my own "Scan with (AntiVirus program)" entry, to see where it is... This may be the alternate method that DropBox globally uses.
I'm just trying to demonstrate that CCleaner only really does everything you can do yourself if you're bothered, but in a different format...
CCleaner lists them under startup entries, but I don't see them in MSConfig. Probably have to manually track them down in regedit.
...yeah, not sure about Add To Dropbox menu items being a Startup thing (unless that's from the internal knowledge that the entirely different "HKLM/SOFTWARE/Microsoft Windows/CurrentVersion/Run" item that initialises DropBox starts a process that aggressively reinstates the shell/ items, whenever removed, which is an ugly practice that should be killed with fire!) in any sane sense... I understand their thinking, but it's giving the wrong impression to the end-user in the interests of conveniently presenting an "I can do it all with fewer clicks" thing that keeps people in awe of the really quite simple process they could use without getting into the habit of installing random programs.
(And I must admit that I never thought I'd describe the registry as 'simple'. I never really got over the whole 9x move away from .INIs! But it's only completely obscure when you don't know what you're looking for, and gets better as you expose yourself to it more.)