Hogwarts Legacy Fluxweed Stem is an ingredient you'll need during your time at the School of Witchcraft and Wizardry. Professor Garlick, the herbology teacher, gives you an assignment to grow some, but you will run into problems if you still need to unlock the Room of Requirement.
You can buy the magical plant, too, so if you only need it to concoct a specific potion you can get hold of it easily enough. If you don't have enough cash, eye chests give you 500 Galleons each, so it's worth opening a few to boost your wallet. Here's where to find Hogwarts Legacy Fluxweed Stem, where to buy the seeds, and how to grow them.
