Democrats are quite good at splitting hairs.
Yeah this is definitely splitting hairs. I suspect that Hur had orders to not declare Biden was chargeable. Biden was found to be blatantly doing illegal acts, so Hur said that he would not be charged in terms that most of the public would interpret as non-compos mentis, or mentally incompetent to stand trial. Normally when this is determined informally by a prosecutor, the accused is already not in a position to commit further crimes (e.g. hospice care).
Republicans are rightfully crying foul as how can someone be both incompetent to stand trial and competent to carry out the duties of President?