Thanks @JasroV ! I now realize that I cannot downgrade my file to be readable by 2018 but I do have 2018 backup except it is from last year just before upgrading to 2020. I now have installed 2018 and restored the file from last year but now I'm missing all last year's transactions. Is there a way to export last year's transactions from the 2020 file and import them into the 2018 file? The link you included talks about import/export of customers and vendors but not the transactions.

Thanks!