I have used some third party tools such as nintex workflows where users can send and email with a keyword approved or yes and the workflow gets approved and status field gets updated.
can i do the same with Microsoft flow ?
Yes, so long as your recipient is using Outlook 2016 or Outlook Web app
Microsoft has named this feature "Actionable Messages".
To implement this, you would add a "Start Content Approval" action in Flow, which will send out approval request emails. All recipients will receive an email that can be approved or rejected (with comments) without leaving Outlook:
Approvers that are using earlier versions of Outlook will still receive the email - however, they will be directed to the Microsoft Flow site to action the request.
The following Microsoft blog post describes in more detail: Respond to your approvals from your inbox and Set an Approval Expiry
Yes, you can do that using a MS Flow.
You can add a condition to classify the keyword value and then start an approval request based on the value.
An official article for your reference:
Create an approval request