Follow these steps to restrict books based on country:

1. Add the restrict_country_ids m2m field in the library.book model, as follows:

class LibraryBook(models.Model):
    _name = 'library.book'
    _inherit = ['website.seo.metadata']

    ...
    restrict_country_ids = fields.Many2many('res.country')
    ...

2. Add a restrict_country_ids field in the form view of the library.books model, as follows:

...
<group>
    <field name="date_release"/>
    <field name="restrict_country_ids" widget="many2many_tags"/>
</group>
...

3. Update the /books controller to restrict books based on country, as follows:

@http.route('/books', type='http', auth="user", website=True)
def library_books(self):
    country_id = False
    country_code = request.session.geoip and request.session.geoip.get('country_code') or False
    if country_code:
        country_ids = request.env['res.country'].sudo().search([('code', '=', country_code)])
        if country_ids:
            country_id = country_ids[0].id
    domain = ['|', ('restrict_country_ids', '=', False), ('restrict_country_ids', 'not in', [country_id])]
    return request.render(
        'my_library.books', {
            'books': request.env['library.book'].search(domain),
        })

Update the module to apply the changes. Add your country in the restricted country field of the book, and access /book. This will not show restricted books in the list.