After enabling the approval workflow feature, you noticed that your form respondents are not able to approve or reject a request. Read this article to understand why.
You activated 'Collect email addresses'
If you have activated 'Collect email addresses' in your Google Form settings:
And checked 'Notify form respondent' in your 'Sharing options & notifications' sidebar:
Then your form respondents will NOT be able to approve/reject the request. They will only be notified once this has been done by approvers (in our example, the approver is 'email@example.com').
How can my Form respondents approve/reject a request?
First, make sure that 'Collect email addresses' is NOT ticked.
Then, manually add a question title for the email addresses, for example 'Email address'.
Finally, reuse it as a marker in the 'Sharing options & notifications' sidebar as shown below: