How can I send monitoring notifications to Google Chat in Google Cloud Platform?

I want to send monitoring notifications to Google Chat in Google Cloud Platform. Under Monitoring > Alerting > Edit notificaton channels, Google Chat is not listed (only the competitor Slack, interesting...).

If I try to use a Webhook, the message never arrives in Google Chat. This is because the webhook request sent by Google has the wrong format - it does not include a "text" key in the JSON body (see here for the format of the request sent by Google).

Is it impossible to send monitoring notifications to Google Chat, even though the competitor Slack is available?

I think the current solution is to implement some script to send notification. I followed this guide and wrote a Python Cloud Function to do the notifications.

StackExchange DevOps Q#12061, answer score: 3