Follow the steps below to enable workflows, like kanban for the book rent model.

1. Add a kanban view for libary.book.rent, as follows:

<record id="library_book_rent_view_kanban" model="ir.ui.view">
    <field name="name">Rent Kanban</field>
    <field name="model">library.book.rent</field>
    <field name="arch" type="xml">
        <kanban default_group_by="stage_id">
            <field name="stage_id" />
            <templates>
                <t t-name="kanban-box">
                    <div class="oe_kanban_global_click">
                        <div class="oe_kanban_content">
                            <div class="oe_kanban_card">
                                <div>
                                    <i class="fa fa-user"/>
                                    <b>
                                        <field name="borrower_id" />
                                    </b>
                                </div>
                                <div class="text-muted">
                                    <i class="fa fa-book"/>
                                    <field name="book_id" />
                                </div>
                            </div>
                        </div>
                    </div>
                </t>
            </templates>
        </kanban>
    </field>
</record>

2. Add kanban in the library_book_rent_action action, as follows:

...
<field name="view_mode">kanban,tree,form</field>
...

3. Add the _group_expand_stages() method and the group_expand attribute in the stage_id field, as follows:

@api.model
def _group_expand_stages(self, stages, domain, order):
    return stages.search([], order=order)

stage_id = fields.Many2one(
    'library.rent.stage',
    default=_default_rent_stage,
    group_expand='_group_expand_stages'
)

Restart the server and update the module to apply the changes. This will enable a kanban board, as shown in the following image: