Shopware 6: Flow broken

I just had a nice discovery: My flow builder was broken, in detail: No actions loaded. Took a moment to realize:

{
    "errors": [
        {
            "code": "0",
            "status": "500",
            "title": "Internal Server Error",
            "detail": "Environment variable not found: \"MAILER_DSN\".",
[...]

So, please make sure the new env variables are set when using flow:

• LOCK_DSN
• MAILER_DSN
• OPENSEARCH_URL (when using elastic or open search)