For scheduler, setting the value worked. But not for debug.
{
"debug": "{{$_ENV.DEBUG_MODE == 'true'}}",
"cron": "{{$_ENV.RUN_SCHEDULER == 'true'}}",
"secret": "{{$_ENV.SITE_SECRET_KEY}}"
}
Scheduler runs as per the value of the ENV variable. But debug is always false when written like this.