I think now more than ever, approval/disapproval ratings have less to do with the reality of any situation than what viewers are sold on their "news" station.
As my wife and I had lunch at a local establishment that airs nothing but Fox, I could see a poll on border security. If you take the third of the country that still supports Trump/watches Fox, it added up nicely to the shift in perception of border security.
Do people really believe all the CBP has been replaced with Biden buddies, standing idly by as anyone and everyone streams across the border? Apparently. Still fearing the non-existent "Middle-Eastern" in the midst of the caravan, and ignoring the porosity of our airspace.