1) Yes, you only need to file Form 1040-X and any forms that change (Form 5329 and Schedule 2) when mailing an amended return.
2) Yes, you can try to e-file the 2020 and 2021 amended returns. Please be aware, some customers had issues e-filing prior years' returns. It is supposed to be fixed by next week. Otherwise, you will have to mail all amended returns.
@ruibing
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