Amending last year’s return while also filing this year’s return

Thanks to all who chimed in on my other post.  I have another question as well, also involving MLPs in trusts.

I’m using Turbotax Business to file a fiduciary 1041 trust return as trustee.  This trust is my mother’s, who passed away in 2018.  I made several MLP investments in this trust in 2020.  Consequently, I had various suspended passive activity losses to carry forward into the next tax year, i.e. 2021.  Unfortunately, 2020 was also my first year using Turbotax Business, so I didn’t realize I needed to check the box that says “Section B1 (Qualified Business Income Deduction)” to have it actually enter the QBI suspended passive activity loss carryforwards in the appropriate fields in Section A.  I belatedly realized my mistake while doing 2021’s taxes, finding nothing there where these should have been.

Naturally, I’d like to fix this.  I assume I'll need to amend my 2020 return and include those carryforwards so I don't lose them.  My question is, how should I handle 2021’s return in light of that?  For now, I’ve filed for an extension.  But can I go ahead and file the 1041 return for 2021 with the suspended losses from 2020 already carried forward, pursuant to the amended return I also intend to file?  Or, should I wait for that amended return to be accepted first before filing 2021’s return?

On a related note, Turbotax says the amended return can’t be e-filed, so what should I do?  Where do I attach the required explanation statement to a paper return?

Thanks for any advice.