It was your father, not you, who had no RMD for 2020. Because your father had no RMD for 2020, there was no year-of-death RMD for you to complete on behalf of your father. Because your father died in 2020, your first year as beneficiary under the 10-year rule was 2021 (not 2020), with 2030 being the 10th year. The account must be fully drained by the end of 2030.
Because your father died after his required beginning date for RMDs, the proposed regulations require you to take annual RMDs under the 10-year rule. However, the IRS has waived through 2024 the penalty for not taking these beneficiary RMDs under the 10-year rule.
