The left dismisses accountability as if Biden was utterly powerless to alter the plan left to him by Trump.

Again, this is not about dismissing accountability. Just dismissing the argument that there would have been any different outcome had Trump been re-elected, rather than Biden.

The Taliban rising to power was the ineluctable consequence of the U.S. withdrawing from the mission of defending the Afghan government. Once the decision was made to stop performing that mission, the Afghan government was going to inevitably fall. And since both Trump and Biden were on the same page that the withdrawal would happen (even assuming arguendo that the Trump Administration would have executed the actual withdrawal better), this is not something that Biden bears any greater responsibility for than Trump (or the other predecessors that created this situation).