I use this command
/data merge entity @e[type=armor_stand,limit=1,sort=nearest] {Invisible:1b,PersistenceRequired:1b}
I used it just last week so it should still work!
Make sure to stand directly next to the the armor stand u want invisible, it's a command for the nearest
i add the persistence because it supposedly keeps the armor stand from de-spawning if you travel great distances
