My previous employer didn’t pay me for couple months last year and also didn’t provide a W2 for 2020. Is this something you can help with?
The W2 should be demanded from the employer via a written request and complaint to the agency (IRS) which requires that the employer give W2 to all their employees by mandated dates. https://www.irs.gov/faqs/irs-procedures/w-2-additional-incorrect-lost-non-receipt-omitted/w-2-additional-incorrect-lost-non-receipt-omitted
You can complain to the WHD of the US DOL for unpaid past wages. https://www.dol.gov/agencies/whd/contact/complaints
Please make sure that you were hired as an employee and not a contractor for this to apply.