Hi,
I see when I set up this computer to with blat-stunnel-gmail, that I ran a line with blat.exe to store the gmail password. I don't see a way to store an app password, but blat is old.
App password == normal password
Google is requesting to use, instead your account password, a generated app password.
So setup it as you did before.
There is no need to change anything on Stunnel.
Regards.