In the flow designer actions, go to any out of the box "Actions"
Steps to reproduce:
1) Login to the instance using "admin" user
2) Go to Flow Designer
3) Click on the Actions tab
4) Open out of the box action like "Add Owner To Group" action
5) Click on Rest STEP action.
6) Try to click on "Enable Retry Policy". It does not get "ticked". See screenshot below:
This is out of the box action which only has "Read Only Action". So, we cannot edit this.
We can create a copy of this action and then edit it. So, on the same action page go to more actions that have vertical 3 dots icon. See below screenshot: