When the Teferi, Hero of Dominaria vanguards attains its emblem, it is able to exile a random opposing card whenever you draw a card. However, it is unable to exile opposing vanguards, even if there are no other cards left to exile.
While on the board Vanguards can’t be affected by effects that don’t specifically name Vanguards. Card is only a general reference to a Vanguard not a specific naming of Vanguards.
This is a difficult one. Cards that remove “supports” have to specifically name Vanguards or else they won’t be able to destroy them. However, Teferi specifically states that word “card” and a Vanguard is definitely a card. So, I would like to hear from @Magic_PQ_Support_Team if this is a bug or working as intended.