If I am past the deadline, and I am due for a return (I've done it on PDFs but didn't file), is there any point in filing?

I downloaded the PDFs for the tax forms back in April, filled them out, and saw I was due for a return. However, I found I could not e-file, and I didn't realize that tax software was as cheap as it is.
I've heard that the 2018 returns could be filed as late as 2020, but I don't know if that applies to all returns or if it was a specific 2020 rule.