The most simple solution to do this, is to add a boolean on the entity: _isEditable. If it is non editable you set it to false. If it is editable, you set it to true.
Then on the fields that should only be editable you set the conditional editability to only be able to edit it if _isEditable is true.
Please be aware that this is good for UX purposes, but not security.
Add Boolean attribute and change it in microflow using change object activity