Could Biden have actually changed the Afghanistan thing? That was actually Trump's decision--and my favorite one he ever made--but he put the timetable into the next presidency just in case of bad press.
I don't believe that's true. He wanted to start orderly withdrawal sooner so that it'd be well underway before the election, but his generals postponed it (and then hightailed out of there in a highly disorderly fashion leaving the Taliban in charge and giving them billions of dollars in materiel).
Biden is the commander-in-chief, yes he could have changed anything about it that he wanted to. He could have gone back to the Taliban with modifications to the terms. They were not in a strong position to resist, frankly. If the US had said they needed three more months to do it effectively, the Taliban would have agreed. Also Biden was making choices along the way related to the time table (Wikipedia covers this fairly well).
You realize Trump was the one who set up the deal and the timeframe for the Afghanistan pull out right? He even bragged about sticking Biden with it. The Taliban were upset when it went over the date and upped their already regular attacks.
And in fact to your last point about trusting America, Biden was trying to stick to the agreed upon deal.
Wrong. Biden welched on the deal Trump made. The same day he did that, Taliban began attacking.
The fustercluck withdraw from then on was all Biden's fuck up. All Biden had to do was honor the previous terms and use the previous plans, then the pull out would have gone off without much drama.