I have the same issue on a realm running 1.17.32.
Placing a new sign will allow you to enter the text and apply it successfully. If i then logout of the world and log back in the sign will be blank.
i did not attempt this in 1.17.30 as i barely used it thanks to the looting bug.
possibly also related to
Confirmed broken on Realms via Xbox.
Trident will despawn after the chunk becomes unloaded.
Confirming bug exists on Xbox realm. Unable to check for local world as don't have any world's with xp farms.
Armour shows as having reduced durability, using my guardian farm for xp and all gear has mending, the durability does not update within the armour slots of my inventory. Swapping the armour to my inventory and back into the armour slot will update the durability.
This affected my legs, boots and elytra slots. I believe it to be a purely visual bug as once i start gaining xp on my experience bar each item showed no change however after swapping out and back in it updates to full durability again.