Make the Withdraw function visible as a button on the observation block (with a connected tool-tip)

Perhaps. Equally, I don’t think it will do any harm though, it would just add further clarity to the UI.

But yes, for me… the main issue to tackle is expressed by a new user on another thread in response to someone asking why she hadn’t used withdraw.

I think this solution would probably help to tackle these instances.
Though maybe it should only appear in case of disagreement, as @pisum suggests.

I think many may still blindly agree afterwards still… even having used a withdraw button. So, I also concur with those who think that the agree button should be invisible to OP - to force them to have to add ID manually (but only on the provision a withdraw button is made visible, to prevent unnecessary disagreements from languishing and thereby adding work to identifiers to overpower).