This is not about transmog. If I go to a transmog vendor I can choose artifact appearances that are in my spec and I have unlocked.
Rather, I can’t change the appearance of the original artifact weapon. When I go to my class hall (paladin) the Altar of Ancient Kings (big stone slab at the front of the “chapel” in the beam of light) is not interactable in any way. It does not have any hover text and the mouse cursor does not change to a different icon indicating you can click the object. This is whether I have an artifact equipped or not. If I open my character sheet and right-click the artifact it shows me the page when I can replace the relics slotted into it, but there is no tab for appearances, even if I’m standing in front of the Altar of Ancient Kings.
Is this a bug, or is this supposed to be disabled at a certain level or after completing a quest chain or final Legion raid or something? I’ve been searching the last few days and haven’t found this mentioned anywhere except one forum post months ago describing a similar issue with no replies.
Other alts that have not completed Legion can use their class hall artifact forges just fine. I also tried on another computer after uninstalling anything Warcraft/Blizzard related and deleting all the leftover folders in program files/program data/appdata, so no cached character data or addons would be interfering.