Consider what he would have to accept if he faced the truth: That his incorrect beliefs directly caused his wife's death.
Not surprising he'd perform basically any level of mental gymnastics to avoid that.
Ego-protective delusions are extremely common and most are motivated by far less than this.
He apparently believes that even though his wife went into the hospital for COVID, she actually died from pneumonia, and not COVID. I guess no doctor explained to him that pneumonia is simply an infection that has spread to the lungs.
You can't help people like this.