Check the links I put above to the stem and cartridges that look like they will fit on amazon. Those off brands use off the shelf parts for the valving that is why they are able to sell them at lower prices. If you search you can find them on ebay, amazon, and cheapest cartridges are on Temu and Aliexpress but it takes 2 weeks to arrive from China so buy an extra one if you go that route.
I think at this point he's already replaced the fixture. I recommended back when he first posted to pull the cartridge and see if it was generic, but I don't think he did.
I would have bought a new one on Amazon, swapped the innards, and returned it.
John