Was this originally taken as a RMD and you are 70 1/12 or older?
If yes, then delete the 1099-R and re-enter. Check the box that says, "None of this distribution was a RMD" (there were no RMD's in 2020). Then the rollover should work.
If not, post back with what happens.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**