For whatever it's worth--maybe nothing--lots of us used to keep chapters as separate documents rather than writing an entire novel in a single document. For old computer with small RAM, it made sense. The file opened quickly, you could move through it without the computer lagging, etc. I wrote novels that way and thought I was being smart.
For the time, maybe I was, but it stopped being a good idea when I edited. Change a character's name? Open every chapter, use Find and Replace twenty-three times. Check that I didn't contradict myself on those two streets that intersect? Sheesh, good luck finding the few chapters that mention street names. Open about twenty of them. Time to minimize adverbs ending in -ly plus a few faves that don't, like just and very? Open all twenty-three chapters, repeat the same three searches. Want to make sure every it's is a contraction of it is or it has? Yup, check all twenty-three. What happened in edits is that what could have, should have been quick look-ups became a long and tiresome process.
Back then, I broke novels into halves. It minimized lag and streamlines edits, revision, and rewrites. Not that I sold the result, but I was learning.
Fast forward to the present. Any computer less than four or five years old can easily handle the text of an entire novel in a single document. It will be a bit of drudge work to create a new document that is this draft of the book and move each document that's a chapter into it, in order. (Or copy and paste it if you worry this won't work, so your originals will be untouches.) But IMO, it's totally worth the effort. I bet you can do it in fifteen or twenty minutes.
I've written all my novels and novellas as one document for years now, and I don't have super-computers or anything. Libre Office will give you the word count of the whole, of course, and if for any reason you want the word count of a chapter, you can just select its text.
Maryn, who also backs up faithfully