I used the "stop sharing an item" action, and I found that the user who triggers the approval flow needs to have a "Full control.' permission.
So, I created a new permission level by copying the "edit" permission and checked these 2 on the site permission, then move the user from "edit" permission to this one.
The result is that the user has an "owner" on sharing the item instead.
The thing that I want is
1. when the flow ends the process, the "stop sharing an item" action work without assign "Full control" permission.
2. I need to stop sharing an item both user and approver. So, the user will not be able to edit/change that item.