Check your second parameter in _convert
It should be record instead of str, try this

to_currency = self.env.ref('base.USD')
...
total = journal.currency_id._convert(
    float(journal.default_account_id.current_balance),
    to_currency,
    journal.company_id,
    fields.Date.today())

Hi, you should try printing the type of all values to check if they are the Required type, in this case float. odoo has functionality of rounding that can be done on float type values. Here an argument of string type is trying to be rounded, that’s why this error is occurring. 

No it did not work.

kindly check:

from odoo import fields, models, api

class AccountJournal(models.Model):
_inherit = 'account.journal'
 
total_usd = fields.Float(string='Total in USD', compute='_compute_total_usd', readonly=True)

def _compute_total_usd(self):
for journal in self:
total = journal.currency_id._convert(float(journal.default_account_id.current_balance), 'USD', journal.company_id, fields.Date.today())
journal.total_usd = float(total)

" rel="ugc">ir.ui.view">
account.journal.kanban.inherit
account.journal