[1.20] Gravewarden Tech missing?

I'm not sure what you mean by this.  There is no Gravewarden tech in the game.  There is a unit called a Gravewarden that is unlocked with the Enchantment tech.  That appears to be working correctly (note you need crystal to train Gravewardens).

In the Tech Tree the Gravewarden unit icon no longer appears in the Enchantment Tech.  However, the a Hallowed Rite ability (which is what I was looking for) is available after learning the Enchantment Tech.