UPDATE, my post is updated with the correct v14 labels and I have requested a documentation update.

This is documented at https://www.odoo.com/documentation/14.0/applications/inventory_and_mrp/inventory/management/lots_serial_numbers/expiration_dates.html

Product configuration

Now, you have the possibility to define different dates in the inventory tab of the product form:

Expiration Time: refers to the number of days before the goods may become dangerous and must not be consumed. It will be computed on the lot/serial number;

Best Before Time: it’s the number of days before the goods start deteriorating, without being dangerous yet. It will be computed using the lot/serial number;

Removal Time: shows the number of days before the goods should be removed from the stock. It will be computed on the lot/serial number;

Alert Time: refers to the number of days before an alert should be raised on the lot/serial number.

Reviewing the code:

https://github.com/odoo/odoo/blob/14.0/addons/product_expiry/models/production_lot.py#L79

... you can see the Activity is assigned to the responsible_id of the product, which is defined on the Inventory tab of the Product:

I have requested the information about who the Activity gets assigned to be added to that page.