Microsoft purview - unable to approve a workflow request

Question

In MS Purview, after creating Approval workflow, the approver successfully gets an email request for an approval for creating a business glossary term, but when the approver goes to the Approval page of the Purview workflow, the response dropdown (shown in image 1 below) is disabled - and hence cannot select Approve or Reject option.

Question: What could be the cause of this issue (dropdown disabled) and how can we resolve it?

Remarks:

1. In our organization, we have two domains, one is for email, say, EmailDomain.com and another domain, say, ITDomain.com where MS Purview is installed. When you login to MS Purview, you have to use ITDomain.com (e.g. you login to Purview as [email protected]). But when you select an approver from a workflow screen (shown in image 2 below), you have to select approver's email address from email domain, for example, [email protected].
2. The approver is a global admin of Purview and is also Workflow Admin in Purview

Image 2 [step 8 of this section]: