Open the file by acknowledging the warning, but so as to NOT activate the links (been a while since I've used such a file, and I don't remember the exact wording).
Once open, follow this path of selections to get to the Document Inspector:
File | Options | Trust Center | Trust Center Settings | Privacy Options | Document Inspector
(So begin with Alt-F or selecting File from the Ribbon Menu, and go onward.)
The Document Inspector offers to look at MANY things, the one of interest being about halfway down (9th choice, for me), that of Links to Other Files. You can uncheck the rest (and if interested, do them later) and run the feature.
Obviously I have not just done so (see above), but it is supposed to be able to show you everything you could wish to see.
My memory also says that when one opens without updating links, a dialog box of standard links that exist in the file pops up. Document Inspector claims it can see more than I remember that dialogue box showing, so that's probably good for you as well.
Separately, yes, there ARE ways to remove links. VBA is one way, and actually, all the kinds of links I've read about needing removed (especially including Named Ranges in general and those with links in particular) involve using VBA to inspect and find them as well as delete them. You should have no difficulty at all finding macros for one kind and another.
After years of using links, and having a couple files ruined "corrupted" according to Excel) when Excel did something and lost track of one or more, I changed methods and when I wished for links, I created a page on which I made simple formulas that brought the would-have-been linked material into the file, onto that page. So then all the links were in simple to locate and to edit formulas, I kept a buffer of columns and rows above and left so none ever lost their references from careless row/column deletion. The spreadsheet's formulas then referred to that data, not directly the source file's data. There was also the advantage that those formulas could always read from an otherwise closed file so functions that could not were not stymied by them not being open as they read from their own file.
Glad all that's over. I just don't need that feature anymore. Something you might consider if you don't want links to other files.
However, that's a lot of work, likely. Inspecting each file and becoming happy with their links would need doing anyway before going to that work. So perhaps you'd prefer to "vet" these files as you encounter them and being happy with them, allowing them to open the links automatically as you open them.
I would say though, that if any of them are files out of your employer's control, or in the control of feckless people in your own company, or in any other way you might find the owner of the file might add unfortunate materials and links that could then feed into your own file, I'd take a different path...
