https://wikileaks.org/gifiles/docs/32/323433_-os-afghanistan-Iran-security-taliban-fighters-being-taught.html
https://www.longwarjournal.org/archives/2010/11/the_taliban_acquisition_of_ant.php
https://www.militarytimes.com/flashpoints/2020/01/14/Iran-support-to-the-taliban-which-has-included-manpads-and-a-bounty-on-us-troops-could-be-a-spoiler-for-peace-in-afghanistan/
If you cannot see why it would make pragmatic sense for Iran to play a double game in keeping Americans bogged down in Afghanistan, the graveyard of empires through sporadic support to the Taliban, and choose to disregard the above links, including from Wikileaks (there is more if you choose to look into the Afghan War papers 2010), then that is on you.
https://en.m.wikipedia.org/wiki/Afghan_War_documents_leak
The leak, which is considered to be one of the largest in U.S. military history,[6][13] revealed information on the deaths of civilians, increased Taliban attacks, and involvement by Pakistan and Iran in the insurgency .[1][14][15]