sass --watch with automatic minify?

There are some different way to do that

sass --watch --style=compressed main.scss main.css

or

sass --watch a.scss:a.css --style compressed

or

By Using visual studio code extension live sass compiler

see more

If you are using JetBrains editors like IntelliJ IDEA, PhpStorm, WebStorm etc. Use the following settings in Settings > File Watchers.

1. Convert style.scss to style.css set the arguments

   --no-cache --update $FileName$:$FileNameWithoutExtension$.css
   

   and output paths to refresh

   $FileNameWithoutExtension$.css
   

2. Convert style.scss to compressed style.min.css set the arguments

   --no-cache --update $FileName$:$FileNameWithoutExtension$.min.css --style compressed
   

   and output paths to refresh

   $FileNameWithoutExtension$.min.css
   

sass --watch a.scss:a.css --style compressed

Consult the documentation for updates:

• https://sass-lang.com/guide
• https://sass-lang.com/documentation/cli/dart-sass#style

If you're using compass:

compass watch --output-style compressed