Power Automate: write Approved or Rejected back to your SharePoint list

Short answer: use the Start and wait for an approval action, then an Update item action on the same list item. Microsoft's page says this action "Starts an automated approval and then waits for it to complete." Set your Status column from the approval result after it finishes.

The list you need

Make these columns on the request list.

Title: the short name of the request.
Status: a Choice column with Pending, Approved, Rejected. Set the default value to Pending.
Approver comments: a Multiple lines of text column.

Build the flow

Work in https://make.powerautomate.com. Exact names may differ on your screen.

Choose Create from blank and open Add a trigger.
Search for the SharePoint trigger When an item is created. Microsoft says it "Triggers when an item is created." Choose the site address and list name.
Add the action Start and wait for an approval from the Approvals connector. Pick an approval type from the table on Microsoft's Learn page. For a single manager, Approve/Reject - First to respond is the simple choice. Sequential approval fits a chain of approvers.
Fill in Title, Assigned To, and Details. Microsoft says Assigned To takes "Email address", "User Principal Name (UPN)" or a Microsoft Entra ID user id, and you "use a semi-colon (;) to separate user identifies."
Add a Condition that checks the approval Outcome. Microsoft's page says valid responses to a Basic or Await all approval type are "Approve" and "Reject". These responses are case-sensitive, so match them exactly.
In the yes branch, add the SharePoint action Update item. Microsoft says it "Updates an item in a SharePoint list." It needs the Site Address, List Name, Id, and Item. Use the Id from the trigger. Set Status to Approved and Approver comments from the approval response.
In the no branch, add a second Update item with Status set to Rejected and Approver comments from the approval response.

Why this flow does not run itself again

The trigger fires only when an item is created. Update item changes an item that already exists, so it does not start a new run. If you switch to When an item is created or modified, Update item counts as a change and the flow starts again. Add a guard before you switch. See "A flow that triggers itself in a loop" and "Trigger only when a specific column changes".

Why the item stays Pending

Check these in the run history.

The Update item never ran. Open the run and look for a skipped or failed step.
The Condition did not match. The Microsoft page says "Approve" and "Reject" are case-sensitive.
The Update item used the wrong Id. Use the item Id from the trigger.
The flow is waiting. Start and wait for an approval holds the run until someone answers. See "Approval timeout after 30 days".

The null outcome error

Open the failed run, expand Update item, and look at the exact value it was sent. If the approval step was skipped, the outcome has nothing to give.

Content approval is a different feature

SharePoint also has a Set content approval status action. Microsoft says it works on "an item in a list or library that has content approval turned on." That is the built-in approval status of the list, not a Status column you made. Pick one. This page uses a Status column.

What to avoid

Do not switch the trigger to created or modified without a guard.
Do not type over the Status column while the flow runs.
Do not type the outcome text differently in the Condition.
Do not send an approval to a group you did not test.

When to get help

You can build all of this yourself in Microsoft 365. If you would rather have it built and tested for your team, I do that. A tracker like this is a fixed price: $5,000 for one, built in 2 weeks. See "What a SharePoint tracker costs to build". Bring one example of the problem to a free call.

Tell me what's still manual

I am Al Davies. I run 250 High Street LLC and build SharePoint trackers and Power Automate flows for operations teams. I work remotely. The first call is free, and I will not try to sell you anything.

See trackers I built: Tools I built

FAQ

How do I update a SharePoint list item after an approval in Power Automate?

Add Update item after Start and wait for an approval, and set the Status column from the outcome.

Why is my SharePoint approval status not updating?

Check that the Condition matches "Approve" and "Reject" exactly, and that Update item uses the trigger Id.

Can the approver add comments back to the list?

Yes. The approval response has a Comments field you can send to a column in Update item.

Does the approvals connector need a premium license?

No. Microsoft says it is a standard connector, so a license with standard connectors is enough.

How do I stop the flow from running twice?

Start it with When an item is created. Update item changes an existing item, so it does not start a new run.