Do you get any errors in the proforma process when you run it in the 2020 software?

Are you sure you don't have any filters (either F7 or the clickable filters on the left panel) set in 2021 so that you just aren't seeing it show up?

If neither of these fixes it, you're probably going to need to call Support.

Check your data path, if none of Karl's excellent suggestions work. 

Try to re-proforma again, and make a note of the default path used by Lacerte.  

Is the 2020 client locked? If so back it up. Unlock it and then do the proforma again.