Default downloads folder

I am using WinSCP Portable (version 5.7.5), which I got from here:

https://portableapps.com/apps/internet/winscp_portable

How can I set a folder that I want WinSCP to always use for downloads by default?

We do not support custom 3rd party build of WinSCP here.

The official build of WinSCP does support portable use out of the box:
https://winscp.net/eng/docs/portable

See also https://winscp.net/eng/docs/faq_dir_default