I get this same message, but I have a construction shell with the camera at the top and no tailgate. I'm guessing you may have an alignment issue, but I have no idea how you might be able to adjust it.
Ford valet service picked up my 21 Lariat 2 weeks ago to do the wiper motor recall and hub bolt inspection while I was recuperating from back surgery. The inspection reported no problems, but I'm wondering if I could still have the issue come up later. Curious what they are looking for.
I constantly use my in cabin outlets to charge my Dewalt batteries on my 21 Lariat. I've never had an issue. I'm an electrician by trade, and it appears to me that you might actually have a grounding issue. I'd check all connections from the inverter up to the outlets.