Socialist Afghanistan
It's the classic good-news, bad-news scenario.
I think the Afghanistani people might have been better off materially without the march of agony after Soviet withdrawal/fall of Najibullah's regime.
In my half-informed opinion, the US backed some true bastards.
Gamalbuddin Hekmatyar and Mohammed Dostum should be on the same cell block in the Hague as Milosevic and Tjudman and the folks behind the Rwandan massacres in the aftermath of the fall of Najibullah.
Not letting those two and their buddies run amok for five years before the Taliban came to power would've saved and improved millions of lives.
Education, health care, and infrastructure wouldn't have imploded as badly as they did once funding dried up with Soviet withdrawal in 1989. However, whomever "won" was not interested in rebuilding the country afterward. The Soviets were in no shape to push to the Arabian Sea.
AFAIK, their goals ranged from squashing Muslim fundamentalists inciting
restive Muslim minorities in Central Asian SSRs to any number of economic goals that failed miserably IOTL.
One thought is that Iran and India would really like to have a gas pipeline and the money from having that go through Afghanistan might have helped Afghanistan rebuild after the carnage. It could just have lined the pockets of the Najibullah regime. Who knows? Hamid Karzai was working on that project with Chevron before he became the local enabler of NATO involvement in Afghanistan.
Too many players did not want a socialist, secular state on their border, Iran and Pakistan especially, regardless of US support/funding. Their secret services would make a brisk trade in relaying opium for guns to fund their pet irredentist groups/coreligionists that would make life miserable for the Afghan regime.
You could have another Myanmar with lots of well-armed, restive minority militias that control the countryside while the ruling oligarchy takes their cut from various scams within their borders and squashes anything that looks like a promising coalition to remove them from power or a Somalia where central authority has collapsed and devolved to a collection of tribal governments with that level of interference in Afghan politics.
Either way, too much money and attention goes to security and not enough to internal development in those scenarios.