The form is based on entity 'User'. The entity 'Food' does not need a userid attribuut. In Mendix this is done with an association. Either 'Food' is prefilled and user can select from a list, in that case the association is a reference set and use a 'reference set selector' widget to add one-or more favorite foods.
Other option is 'Food' a private list per user with user added data. In that case the Food entity has a association type 'reference'. Add a datagrid on the user form and select the association Food_User. Right click on the 'New' button and select 'Generate form'. User has to press 'New' to add a favorite food.
To get exactly your form, create an attribute 'FoodToAdd' on 'Account' or (better) your inherited user entity. Put it on your form and add a microflow button behind it with text 'Add' connect a microflow with that button and pass the account as parameter. In the microflow: create action with entity Food. Assign Account/FoodToAdd to Food/Name and Food_Account with Account. Clear the FoodToAdd attribute with refresh/don't save.