Pigsteel is available for 1.21.1 and 1.21.5 on Fabric and there is also a Neoforge port. See it on Modrinth
Mining in the nether just got slightly better with Pigsteel. Porkslag blocks can be found underground, and when mined they drop pigsteel chunks. These chunks can be made into decorative blocks that zombify in the overworld, or they can be smelted into iron nuggets.
Mods that add ore generation to the nether often feel out of place for me, but Pigsteel in the Nether just feels right.
I don't know about you, but I always need more iron (unless I lock a couple of villagers up in a small space and endlessly scare them with a zombie). Pigsteel gives one more way to gather some iron.