Blizzard confirmed ensemble unlocks are not changing in Dragonflight and buying ensembles you cannot equip is a bug.
A few days ago, we wrote about the option to unlock transmog ensembles for alts in Dragonflight. However, Blizzard confirmed this as a bug and not intended in a blue post today.
Currently, there is a bug with Dragonflight vendors that are causing them to show more ensembles for sale than they should to the character viewing their wares. Ensemble unlocks are not changing in Dragonflight; the vendors should only offer them to characters with the appropriate armor type.
With that said, we recognize players don’t want to have to re-earn the ability to purchase these ensembles, but we don’t want to create a problem where a player might unintentionally purchase an ensemble of the wrong armor type, use it and then not find the armor they thought they just unlocked. So in Dragonflight, the ability to purchase the cosmetic Renown unlocks will be unlocked account-wide and can be purchased with alt characters on the account that match the ensemble’s armor type.