For your reference
https:// quickbooks.intuit.com/learn-support/en-us/help-article/regular-payroll/unrecoverable-error-general-troubleshooting-steps/L0sVvm9yp_US_en_US?uid=l6axxz99
If the error message persists, try reinstalling your QBD 2020 and install the trial version for QBD 2021 to compare.
