The $800 duty-free exemption for purchases by returning travelers is different from the de minimis import tariff exemption. The traveler's duty-free exemption is still in place.
https://www.help.cbp.gov/s/article/Article-1402?language=en_US
As it should, because the 249 grams marked on the Mini 4 Pro regular battery refers to the takeoff weight when installed in the Mini 4 Pro, not the M5P, because the only battery which is light enough to come close to 249g in the heavier M5P...
Ok, after watching this on a 50" screen, I'll retract 99% of what I said about the editing being a bit shaggy. I'm really impressed with this video. Amazing. There's some very nice drone flying.