When to use SQL Foreign key using peewee?

I'm currently using PeeWee together with Python and I have managed to create a decent beginner

CREATE TABLE stores (
    id SERIAL PRIMARY KEY,
    store_name TEXT
);


CREATE TABLE products (
    id SERIAL, 
    store_id INTEGER NOT NULL,
    title TEXT,
    image TEXT,
    url TEXT UNIQUE, 
    added_date timestamp without time zone NOT NULL DEFAULT NOW(),
    PRIMARY KEY(id, store_id)
);


ALTER TABLE products
ADD  CONSTRAINT "FK_products_stores" FOREIGN KEY ("store_id")
        REFERENCES stores (id) MATCH SIMPLE
        ON UPDATE NO ACTION
        ON DELETE RESTRICT;

which has been converted to peewee by following code:

# ------------------------------------------------------------------------------- #
class Stores(Model):
    id = IntegerField(column_name='id')
    store_name = TextField(column_name='store_name')

    class Meta:
        database = postgres_pool
        db_table = "stores"

    @classmethod
    def get_all(cls):
        try:
            return cls.select(cls.id, cls.store_name).order_by(cls.store)
        except Stores.IntegrityError:
            return None




   # ------------------------------------------------------------------------------- #
class Products(Model):
    id = IntegerField(column_name='id')
    store_id = TextField(column_name='store_id')
    title = TextField(column_name='title')
    url = TextField(column_name='url')
    image = TextField(column_name='image')
    store = ForeignKeyField(Stores, backref='products')

    class Meta:
        database = postgres_pool
        db_table = "products"

    @classmethod
    def get_all_products(cls, given_id):
        try:
            return cls.select().where(cls.store_id == given_id)
        except Stores.IntegrityError:
            return None

    @classmethod
    def add_product(cls, pageData, store_id):
        """
        INSERT
        INTO
        public.products(store_id, title, image, url)
        VALUES((SELECT id FROM stores WHERE store_name = 'footish'), 'Teva Flatform Universal Pride',
               'https://www.footish.se/sneakers/teva-flatform-universal-pride-t51116376',
               'https://www.footish.se/pub_images/large/teva-flatform-universal-pride-t1116376-p77148.jpg?timestamp=1623417840')
        """
        try:
            return cls.insert(
                store_id=store_id,
                title=pageData.title,
                url=pageData.url,
                image=pageData.image,
            ).execute()
        except Products.DoesNotExist:
            return None
        except peewee.IntegrityError as err:
            print(f"error: {err}")
            return None

My idea is that when I start my application, I would have a constant variable which a store_id set already e.g. 1. With that it would make the execution of queries faster as I do not need another select to get the store_id by a store_name. However looking at my code. I have a field that is: store = ForeignKeyField(Stores, backref='products') where I am starting to think what do I need it in my application.

I am aware that I do have a FK from my ALTER query but in my application that I have written I cannot see a reason why I would need to type in the the foreign key at all but I would like some help to understand more why and how I could use the value "store" in my applciation. It could be as I think that I might not need it at all?