How can I find a particular text between 853 keynote files?

Whether the Finder search window, or Spotlight panel, there are keywords that you can use to avoid searching non-keynote files, and narrowing your search results:

I have a keynote file buried in my filesystem. It has "data-driven" in its slide text. The following finds only that keynote file:

kind:key data-driven

If you are searching for more than one word, for instance, instead of data-driven, but data driven, then you must use double-quotes to surround the white-space as "data driven"

Check Spotlight settings as follows:

go to: Apple menu > System Preferences > Spotlight

• in the Privacy tab, remove any folders listed by selecting the item then clicking the minus button

• in the search results tab, ensure there is a tick next to presentations

I have Keynote v9.1 on macOS 10.14.6 (18G103).

In a new presentation template, I removed the two text boxes, and added a table. I entered a unique string in that table and saved the .key file to my Desktop. Immediately thereafter, I opened the Spotlight panel and entered that unique string of text. That keynote file was found immediately under Presentations.

The Spotlight meta data name for Keynote (.key) files since at least 2010 is not Keynote Document, but rather Keynote Presentation. I have looked at your Drive images and I see it finding campuses which was your search term.

Does the following Spotlight panel syntax discover the keynote document that has George and campuses text strings in it? A match may show you the actual slide containing these strings.

kind:key (George AND campuses)

If there are restrictions due to file size, I am unaware of it, other than the time it would take Spotlight to scan that those huge files for the sought words. What may be happening is Spotlight has internal timeout period that may be exceeded due to these large file sizes. Don't know that for certain though.

open a Finder window

preferably search in a specific folder by clicking that folder to select

click on that folder in the search bar

type in the text that is contained in Keynote