But then it says "field current_year doesn't exist". I have another option where I could just strip each piece from Odoo's datetime field but to me looks performance expensive doing stripping where I may have easier ways.

Ok. Your issue is clearer now. Try this:

from datetime import datetime
from odoo import models, fields

class MyModel(models.Model):
_name = 'my.model'

current_year = fields.Integer(string='Current Year', default=lambda self: datetime.now().year)

Big UP Bro! It really worked! But I have this problem that year 2023 is with a comma as 2,023. I have searched and tried like "widget='integer' " and also added the format options but it didn't work too. How do I solve this?

You can edit the field to Char. Try this:

current_year = fields.Char(string='Current Year', default=lambda self: datetime.now().year)

Bless you my friend! It worked like a charm!