Guys, with a guildie we found out that the problem isn’t the Vellum.
If you notice, the recipes say that you need a RUNED ENCHANTING ROD… and there’s no info about how or where to get that:
https://i.imgur.com/Xghsyxc.pngI assume it’s a rod that will be available to make once the Dragonflight enchanting tier is released.
Buy an Ultimate Gnomish Army Knife in the AH and the problem will be solved 