This is more sudo question than WinSCP question.
See sudo man page:
https://man7.org/linux/man-pages/man8/sudo.8.html
There are the -U and -u switches to specify the target username.

I have run around and around with the different options in the FAQs and forum posts. None of them fit my situation closely enough for me to adapt.

If I use PuTTY, I log in with a ppk RSA key file. Then I use sudo su - userid to change to the higher privileged user. When I do that command, I do NOT have to enter a password.

So, for the SFTP setting, there is a sample that reads like
su -c /bin/sftp-server so that's missing the userid and the sudo.

There is a popular link on StackOverflow that shows:
sudo su -c /usr/lib/sftp-server which is still missing the userid.

I thought it might be a formatting problem, so I created a script with just

in it and it worked to connect as my normal user. If I added the sudo line like this:

then it just hangs

So my question is: Can I do the equivalent of sudo su - userid and then launch sftp-server?