For Markdown and plain-text users, this has long been possible, thanks to how easy it is to scan through plain-text for markers and save each chunk to a new file. And that script can also use Pandoc to convert the chunk to .docx or whatever, so the fact that one starts out with plain-text doesn’t necessarily mean that’s the intended result.
For splitting word processing files though, it’s a lot messier to do that because they are comparably so complicated (.docx files are in fact a .zip file with a bunch of folders and files, kind of like an ePub). There are probably programs you can find that do that, but good luck finding them amidst the festering swamp of “Free Online Document Splitter!” websites that are surely funding themselves by scraping your data and selling it on to language model trainers or advertisers.
In fact if you search for split docx file -online -free macos to weed out all the garbage, guess what search results come up to the top? Scrivener’s Import and Split command. 
Well, while on that topic, there is one kind of silly but absolutely workable Scrivener-only solution:
- Compile using a Format you’ve set up to insert separators with a clear marker at each file split point. Something like 50 hyphens instead of a typical page break.
- In a new blank disposable project, use
File ▸ Import and Split...and designate the 50 hyphens (or whatever) as the split marker. - Select the whole lot of binder items and use
File ▸ Export ▸ Files...to you preferred format.
That wouldn’t be too much of a bother to do now and then, but I’d probably look for something a bit more efficient if this was needed frequently.