According to this, Redis is supported: https://github.com/crowdsecurity/php-remediation-engine/blob/main/docs/USER_GUIDE.md#redis-cache-dsn and the Drupal module implements the feature, however I'm seeing this error:

CrowdSec\RemediationEngine\CacheStorage\CacheStorageException: Error when creating Redis cache adapter:Invalid Redis DSN: parameter "dbindex" must be a number. in CrowdSec\RemediationEngine\CacheStorage\Redis->__construct() (line 35 of /opt/drupal/vendor/crowdsec/remediation-engine/src/CacheStorage/Redis.php). CrowdSec\RemediationEngine\CacheStorage\Redis->__construct() (Line: 198)

It would appear that RedisTrait.php doesn't really expect a tls://?

Moved upstream from: https://www.drupal.org/project/crowdsec/issues/3522049