Only allow the creator of the item and the user direct manager to view the submitted item

johnjohn-Peter 

No - it is you that's misunderstanding, but I'll explain with images so it's clearer for you.

1. Create a custom permission level in Permission Levels

 - Click on the Contribute permission level, then scroll down and click on the Copy Permission Level button

 - Give it a name e.g. Create and View only, uncheck Edit Items and Delete Items, then click on the Create button at the bottom

 - Now you will see a new permission level listed

2. Go to your list settings and select Permissions for this list

• You need to make sure there are two permission groups. One for admins (1 or 2 people with Full Control permission), the other for everyone or specific people, it doesn't matter which. Your flow (needs to run under one of the users in the Owners group).
• For the everyone/specific people group, you need to modify the permissions as shown below and grant that group your new custom permission level:
  
  

  In my example, the Owners group contains the admins (people like you or your SP admin).

  I've changed the Visitors group permission level to the custom permission level that was setup in Step 1

3. Go to List Settings > Advanced Settings and configure the settings as below:

So as of now, with this setup, NOBODY can see any list item unless they created the list item no matter how long your flow takes to trigger.
Furthermore, the creator of the list item can only view it. They cannot delete it or edit it because of the restricted permission level

4. Now you can use a flow that is running under someone in the Owners group or a service account, exactly as described by grant_jenkins with a trigger of When an item is created to add item level permissions, by breaking permissions inheritance (I also remove all permissions except the owners group), and then:
 - Granting READ permission back to the original creator
 - Granting APPROVER permission to the approver
 - Notify the Approver of a pending approval request

Approver 1 will only be able to view the item and approve/reject it.
When Approver 1 has approved, set the permission for Approver 1 to Read. Approver 1 will then only be able to view that item (or you can remove their permission if required).
Repeat the process for Approver 2

I have used this technique for years and I hear this question come up many times and advise the same solution.

If you are not sure how to do the flow part, shout.

I don't think you need anything except:
- A permission group with a custom permission level that allows you to Create & View only. You can add specific people to that group or everyone, it really doesn't matter.

- Configure the list as you have (Users can only see items they create)

- The flow can take care of permissions when a new item is added and during the approval process in the same way as described by grant_jenkins and by assigning Item level permissions

You already have a flow that is triggered when the form is initially submitted and you have the creator, approver 1 and approver 2 details.

So in your flow, remove all permissions on the item and set read permission to creator, approver 1 and approver 2

(Typically you would use a service account or an account that has full control permission to the list)

I think the new List Form will get what you're after.

You can have the list setup so only admins have access to it. Then you can create a List Form that allows users to submit items to the list - note that when using the new List Form the user doesn't need access to the list to submit items. The user just needs the link to the List Form, so you could add this as a Quick link on a SharePoint page.

Then, once the item has been added (only admins have access at this point) you can run your Flow to add permissions (read) to the user that submitted the item, and permissions (approve - or similar) to the user's leader. Then, if the leader approves it, reset their permissions to read, and add the next leader with the appropriate permissions, etc.

This should provide everything you're after based on the requirements you listed in this post.

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