Long story short, before I forget; let me jot down what I did
Connected my Mac Mini to the Windows Laptop network (same wifi -- that's important) and shared a folder on Windows E drive with the Mac, which was read/write on the Mac.
Then in WinSCP, I configured the "storage" (it's under preferences) and ensured that the temp folder that WinSCP creates is on that E drive somewhere, which the Mac can also read/write
Now I run WinSCP on the windows machine ... Login into the server I want, double click on the file and it loads the file in VSCodium (I like that better than VSCode) ... of course on Windows
Now on Mac, I configured the VSCodium there to open the same parent folder that WinSCP had created the temp file in.
Now I can code either on the VSCodium on the Mac or on VSCodium on the Windows! No issues.
The reason for coding on the Mac is that it is more comfortable: Its connected to my 48inch hi-res TV and so I can stand up and work on the Mac Mini -- or sometimes when I am at my Windows machine, I can do that on the VSCodium there too.
Why all this? Because WinSCP has a clever way to deal with SCP - after it logs into a sudo user (such as bitnami on a Lightsail server at Amazon), it silently passes on "su -s" to upgrade the connection to root. So when I save files in another folder on my linux servers (which is not under bitnami username -- usually, that is under www-data) the server does not barf on me.
Something none of the Mac SFTP clients seem to have figured out. Which is quite strange.
Hope this helps someone who reads my blog