Your parent is in denial. They’re obviously not really so brain-dead not to know better than what Trump claims and the other garbage that they encounter about him online and on tv that supports him, but they believe it nonetheless because they want to. Because it supports their worldview. Because, over time, they’ve become so invested in him that to back out now would shatter their entire reality. They’re trapped.
But, as you have seen, for some, reality will slip through the cracks from time to time. The Herculean effort of maintaining such a massive, complex, and, frankly, ridiculous mountain of absurd and outrageous lies for so long is, honestly, exhausting. Nobody could be expected to even keep track of them all let alone maintain the mask 24/7/365 forever. Even Trump slips up and tells the truth when he’s blathering at his Nazi campaign rallies. Just yesterday, he admitted that he did, in fact, try to get to the Capitol on Jan 6 to attend the rally after denying it for over a year, lmao.