"I Think the broker should’ve done two separate 1099R one for 2020 and one for 2021"

No. The 1099-R is for the Distribution event. There is one Reporting for that year. Once the money is in the account(s) it is not segregated by year. The 1099-R is an annual report.

Yes, if both amounts went into the Trad IRA account at the same time, both as nondeductible, for this one taxpayer (but the contributions would be reported in different tax years) and then the entire amount was immediately converted to Roth, so there are no earnings (no gain or loss), and there are no other sheltered tax-deferred amounts (the Form 8606 has a line where you enter the FMV of those similar accounts) and this means $12,000 was converted, and that would have been direct, so no withholding, then you have $0 taxable amount.