Not able to change updateable condition in pagelevel Activity Object

Summary: The updateable option for text field is read only on Activity Page level.

Content (please ensure you mask any confidential information):

We have created a text field in the 'Activity' object from the Application Composer and added it in the TASK details page respectively.

we wanted to make the field Read-only only from the PAGE-Level instead of field level. But we could see that there is no way to do that. It's directly set to 'YES' and there is no option saying : Yes, No Expression for the Updateable option for the field either on the Creation page and Details page.