I think I found the answer here...I think we've missed the timely election date, which should be the QRT's first Form 1041 return deadline, even there were "no sufficient income to require to file that return" per CFR Section 1.645-1(c)(1)(ii).  

https://www.law.cornell.edu/cfr/text/26/1.645-1

It seems to me that this provision defined that the Sec. 645 election due day in this case has nothing to do with the FL 2021 deadline, because it was due April 2020 - even with no taxable transactions back then, we should have filed a zero information return.  We missed the valid election due day. 

I guess our only option now is to file two Form 1041s for both the revocable trust and the estate trust...

I hope to run this thoughts here and see if anyone have different view...Thank you!