Multi theme nextjs - next.js

Question

I am building a multi theme application as it will be deployed on different urls using different themes.
My idea was to use an env variable, in my case APPLICATION_VERSION which can be v1, v2 or v3
I am passing the variable to my sass using next.config.js
const { i18n } = require('./next-i18next.config');
/** #type {import('next').NextConfig} */
const nextConfig = {
reactStrictMode: true,
i18n,
sassOptions: {
prependData: `$theme: ${process.env.APPLICATION_VERSION};`,
},
env: {
APPLICATION_ENVIRONMENT: process.env.APPLICATION_ENVIRONMENT,
APPLICATION_LOCALES_KEY: process.env.APPLICATION_LOCALES_KEY,
APPLICATION_VERSION: process.env.APPLICATION_VERSION,
}
}
module.exports = nextConfig
Then in my scss I created a mixin
#mixin isTheme($value) {
#if $theme == $value {
#content;
}
}
In local this is working with some issues, when I am changing the APPLICATION_VERSION value I have to edit all my *.module.scss files so the isTheme mixin is taken into account.
I tried to deploy it with vercel and seems that the isTheme mixin is ignored
This is my build script where vars are passed
#!/bin/bash
rm package-lock.json
npm i
node ./bin/locales.js
npm i -g vercel
DEPLOYMENT_URL=$(VERCEL_ORG_ID=$VERCEL_ORG_ID VERCEL_PROJECT_ID=$VERCEL_PROJECT_ID vercel --confirm \
--token $VERCEL_TOKEN \
--build-env APPLICATION_ENVIRONMENT=staging \
--env APPLICATION_ENVIRONMENT=staging \
--build-env APPLICATION_VERSION=$APPLICATION_VERSION \
--env APPLICATION_VERSION=$APPLICATION_VERSION \
--regions fra1 )
vercel alias set $DEPLOYMENT_URL $APPLICATION_URL -t $VERCEL_TOKEN --scope $SCOPE
But when deployed threw vercel the content of isTheme mixin is not displayed