Make fields read only for selected users in InfoPath

Step 1)

Create an empty task list

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Step 2)

To make our custom changes to the tasks list we need to customize the InfoPath.

To customize the form, go to the Ribbon menu, click the List > Customize form  

Tasks list InfoPath form opens up in InfoPath designer

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Step 3)

Create two fields namely Initiator (To get the initiator of the form) and Hidden assignee (To get the assigned person)

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Step 4)

To add the created by date to the initiator use username () function in the fx of the field.

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Step 5)

Add the assignee account id in the fx of the hidden assignee field.

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Step 6)

Apply the below formatting rules to make the required fields editable only for the initiator

Create a formatting rule on the selected field with condition

If the Initiator does not contains the username () à Disable the field.

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Step 7)

Apply the below formatting rules to make the required fields editable only for the assignee

Create a formatting rule on the selected field with condition

If the Hidden assignee does not contain the username () à Disable the field.

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Step 8)

Publish the form and test with by creating a new task list item.