Iran does support Pakistan on Kashmir it still does it has infrastructure of support among the Shia there
This is false information.
Pakistani Azad Kashmir has more element of Shias than does Indian Occupied Kashmir (to the displeasure of India,) but still India was trying to use sectarianism to its advantage. They have successfully gained some support from a few Shia areas, and a major Shia family, Abdullahs of Kashmir, who before 370 were big supporters of BJP/RSS.
Iran is deathly fearful of the rise of Taliban (i.e. Pukhtoons) in Afghanistan, and has done everything it can post-Soviet withdrawal to either keep Afghanistan in perpetual state of war or to bring in a Tajik/Shia government under Iranian puppets. They were even willing to share their puppets with Americans and Indians to cause harm to Taliban (.ie. Pukhtoons) and Pakistan (whom they also view in the guise of an enemy, as a supporter of Pukhtoons.)
This is why 1999 was a nightmare scenario, when Taliban leaders met with Pakistan to discuss some kind of merger of both countries. At the same time, Taliban had taken out Iranian spies in major Afghan cities which were providing intelligence for NA enemies, this led to Iranian buildup on the Afghan border which almost led to war.
2001 provided the perfect cover to eliminate that enemy, Iran gave all the sites of Taliban bases and command centers to the Americans and cooperated fully (just like they would later do in Iraq.) Pakistan was forced to betray its former ally due to the united pressure of the whole world, including most Muslim countries, but even then we refused to provide information of Taliban locations. A useless war ensues for Afghans and Pakistanis who lost 100,00+ and 75,000 respectively. Now the world is back to negotiating with Taliban which was Pakistan's position from day one.
This Iranian sectarian regime will try to flare up sectarian animosities anywhere it can, in the hopes of propping up loyal Shia puppets wherever it can. Where impossible, such as 87% Sunni Pakistan, they will cause mayhem and anarchy by using their sectarian forces to launch attacks on the state or cooperate with the enemies of Sunni states to form a nexus against them (how they brought India into Chahbahar and Afghanistan.)
Iran, just like KSA/UAE, is no friend of Pakistan or the Kashmiri cause. They have been willfully silent (except for a few minor statements,) and will be for the foreseeable future.