My K-1 provides allows downloading of a turbotax.txf file that it claims canoe imported by TurboTax but I don't see an option anywhere in Turbotaxonline to this K-1 file

You need Turbotax premium or higher to import a k-1. go to the file tab select import>from accounting software>highlight other financial software (TXF file). click continue and locate the file.  highlight it and then click import now