What's confusing here is that desktop Linux almost doesn't have "regular users". You're a power user already if you are running apt, much less curl|bash. It's not super meaningful to ask what the small number of "regular" desktop Linux users are doing; what is meaningful is to ask what they would do if they existed.
Which is probably the same thing they do on Windows: use a browser to download and run whatever program claims to do what they want.
Ubuntu has an app store (a graphical interface to apt at the time), when my grandpa was running Linux that's what we taught him to use (not often did he install anything though: libreoffice, an email client and a browser was pretty much all he needed)
Which is probably the same thing they do on Windows: use a browser to download and run whatever program claims to do what they want.