Good idea. Now I just need to find where I holed that stuff away to 10 months ago lol

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Hopefully the packet of plugs (maybe 5" x 10") is still in your glovebox or console.
When you do to experiment, perhaps do it one plug at a time. And, do all this with your tailgate lowered which would simulate it being removed compared to being secured up in place.
Since yours is a '23, start with unplugging the small tailgate backup camera connector (light blue) and adding the blank plug there (which I think is brown), then starting and seeing how your cameras are effected. One would expect only the backup camera area to go blue and all your other cameras still work. If not, then you have the '23 camera issue. Informationally, plugging in a replacement backup camera will resolve the issue with the other cameras not working when the backup camera is unplugged, but like I mentioned, I think an update corrected this, so hopefully all your other cameras continue to work even with the tailgate backup camera unplugged and blank in place.
Then there are the two large, 2.5" wide plugs (one gray and one black). See picture in this post:
https://www.fordtremor.com/threads/24-owners-who-removed-tailgate.18096/#post-377326
Those are the two connectors where the short tailgate kit harness goes between and seems to be the one that is not working to tell the computer the tailgate position can be ignored and allows the "tailgate ajar" message. This harness was working fine for all '23 owners as far as I know.
To test, first unplug those connecters without adding the harness and start pickup. You should get the tailgate ajar message as well as little red ajar light in the lower right of your gauge display. Shut off truck, add in the "tailgate removed" harness between those two plugs, start truck again. Hopefully you will NOT receive the Tailgate Ajar message.
There are two or three other medium sized connectors (depending on your options). None of those have seems to give trouble, but they must be unplugged when you remove tailgate and the "tailgate kit" has blank connectors for those as well. If all your above tests work, might as well disconnect those plugs and start truck to see if anything else weird happens, but no need to put the blanks in those during this short test as the blank is just to protect the end of the connector long term while driving. Like the blank plug for the backup camera, for these three connectors, the plugs don't "jump" anything; just cover the open connector.