Sass-loader error 'options has an unknown property 'indentedSyntax'' when upgrading Vuetify from 1.5 to 2

I had the same issue and fixed it by downgrading sass-loader by setting

"sass-loader": "7.3.1",

in package.json.

This was suggested on the Vuetify Discord

vue.js sass vuetify.js

Actually you are using sass-loader 8+ and it has an option a little bit different.
Try using prependData instead of data.
Check this github issue

module.exports = {    css: {      loaderOptions: {        sass: {          prependData: `@import "~@/sass/main.scss"`        }      }    }}

vue.js sass vuetify.js

Update for those using version 10+. prependData is no longer valid. However you can use additionalData as a drop-in replacement.

CodeHunter