I was in the same situation last week, and i got my situation straighten out 
I live in Germany as well, and I didn’t file for 2018 because i was a student and earned too little to file. But due to the coronavirus stimulus that I would like to receive, i filed my 2018 tax return via mail. Turbotax has an option that lets you download a software and fill out your 2018 return, and then print out the return to mail (you can’t e-file for 2018 and later returns)
