@Opus 17 @macuser_22 Thank you for your explanations. I guess the backdoor Roth doesn't quite work for my situation since I can not roll my IRAs into a 401k account w/o some hustle.
I guess now I need to ask Fidelity for the balance of my Rollover IRA account at the end of 2020. I don't know why they didn't provide a 5498 for it.
