Proposals

[hussain]

In settings using _inherit = 'res.config.settings' we add more fields in which those fields may conflict with existing Odoo standard or other modules.
Generic names like purchase_journal_id is problematic, if our cutom module is Employee Bill Claim then we should use a prefix ebc_ for our fields names in settings.
so the generic purchase_journal_id becomes ebc_purchase_journal_id

Also avoid prefix default_ since this is Odoo reserved prefix.

[hussain]

Avoid using:

claim.state = 'draft'
claim.manager_approved_by = False
claim.manager_approved_on = False
claim.accountant_accepted_by = False 
claim.accountant_accepted_on = False

and use write({...}) instead:

claim.write({
    'state': 'draft',
    'manager_approved_by': False,
    'manager_approved_on': False,
    'accountant_accepted_by': False,
    'accountant_accepted_on': False,
})

this is to have single DB call instead of many for the same result.

[hussain]

in py code using domain, always usage of textual values because they are considered harde-coded values.

Bad Example:

def _get_type(self):
    # Get document type
    doc_type = self.env['my_model.type'].search([
        ('name', '=', 'Type - 1')  # ❌ PROBLEMATIC: Hardcoded English string
    ], limit=1)
    return doc_type

Instead use id which is most of the time is xmlid coming from prefiled data using data.xml in module.

Good Usage:

def _get_type(self):
    # Get document type
    doc_type = self.env.ref('my_model.document_type_1')
    return doc_type

[t-saeed]

⚠️ Never modify standard Odoo core files.

All customizations must be implemented through separate custom modules.
This rule is critical to maintain system stability and upgrade compatibility.
AI agents must explicitly exclude these files from modification.