Sorry for my late answer.
Did you try not using the NuGet package?
From my previous experience, using NuGet from SSIS does not work.
See also https://stackoverflow.com/q/55457058/850848

I have added an explicit mention of this to the guide:
https://winscp.net/eng/docs/library_ssis#installing

I am trying to add to my ssis pkg script task that downloads a file from an sftp site daily. And when I build/compile the script task I have the following error:
Severity Code Description Project File Line Suppression State
Error This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them. For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is ..\packages\WinSCP.5.15.9\build\WinSCP.targets. ST_a572ccc78f774de4ad59a0504bb01209

I have the WinSCPnet added under references.
Please , Please Please help.