해당 스레드를 확인해 보았는데, 제가 볼 때 제 설정은 맞을 것 같습니다:
DISCOURSE_CDN_URL: https://thrivecommunity-cdn.b-cdn.net
DISCOURSE_USE_S3: true
DISCOURSE_S3_REGION: eu-central-1
DISCOURSE_S3_ENDPOINT: https://s3.eu-central-1.wasabisys.com
DISCOURSE_S3_INSTALL_CORS_RULE: false
DISCOURSE_S3_ACCESS_KEY_ID: aaaa
DISCOURSE_S3_SECRET_ACCESS_KEY: aaaa
DISCOURSE_S3_CDN_URL: https://thrivecommunity-uploads.b-cdn.net
DISCOURSE_S3_BUCKET: thrivecommunityforum
DISCOURSE_S3_BACKUP_BUCKET: thrivecommunityforum-backup
DISCOURSE_BACKUP_LOCATION: s3