Hello philjun,

Here you go!

You need to follow these two steps.

Solution : 1 (In this solution your sequence field will be editable)

Step1 : Add sequence record in your module.

     <!-- Record for your seuqence type -->
        <record id="your_custom_sequence_type" model="ir.sequence.type">
            <field name="name">Label of your sequence code.</field>
            <field name="code">test.test.code</field>   <!-- Unique sequence code.-->
        </record>
        
    <!-- Record for Sequence-->
        <record id="student_reg_sequence" model="ir.sequence">
            <field name="name">Student Unique ID</field>
            <field name="code">test.test.code</field>  <!-- Apply the same you applied above-->
            <field name="prefix">%(year)s/</field> <!-- optional-->
            <field name="suffix">%(month)s/</field> <!-- optional-->
            <field name="number_next_actual">20000</field> <!-- optional, if you not add this field by default 1 will be starting no. -->
            <field name="padding">5</field> <!-- optional-->
            <field name="implementation">no_gap</field>
        </record>

Step 2: Add field in your model, in your case product is model

    _inherit = 'product.product'
    
    _columns = {
    'sequence':fields.char("Sequence")

    }

    _defaults = {
    'sequence':lambda self, cr, uid, context:self.pool.get('ir.sequence').get(cr, uid, 'test.test.code'),

    }

Solution : 2 (If you want to make your sequence field readonly than you can follow this solution.)

Step 1 : This is same as Solution 1.
 
Step 2 : # inherit model and addd field with readonly attribute

    _inherit = 'product.product'
    
    _columns = {
    'sequence':fields.char("Sequence", readonly=True)

    }

    def generate_sequence(self, cr, uid, ids, context=None):
            
        # This line will generate next sequence number from your seuqence.
        next_seq = self.pool.get('ir.sequence').get(cr, uid, 'test.test.code')

        self.write(cr, uid, ids, {'sequence':next_seq}, context=context)

        return True

Step 3: add button in product form

      <button name="generate_sequence" type="object" string="Generate Sequence"/>

There are many more option to create sequence these two solution will satisfied your needs.

Hope this will helps you.

Regards
Anil Kesariya