This utility can erase the NOR on the EZ Flash 3-in-1. I cannot confirm that it works with other NOR-based Slot-2 cards. If you erase as little as 4 blocks, your DS will no longer show a GBA Game in Slot-2.
Still playing through Breath of the Wild lol, went on hiatus on that game from 2017 until like 2023 cuz I was 12 and I lost the cartridge lol. Picked it up again almost 2 years ago and I'm mostly through it, great game