spec VS PowerPlatformConnectors

The structure of this example message is using CloudEvents specification:

Microsoft has expanded the Event Grid capabilities to enhance system interoperability by introducing support for MQTT v3.1.1 and v5.0 protocols. This allows customers to publish and subscribe to messages for Internet of Things (IoT) solutions. This new support, currently available in public preview, complements the existing support for CloudEvents 1.0.

You are looking for https://cloudevents.io/ . That is what you should use if you plan to do homegrown. I would however recommend you to use use segment + amplitude, juno, mixpanel . If you are early these are mostly free up to a point.

When modeling an event in a streaming application, what "meta" fields to you use? Like timestampts, versions, some context etc... I think there are some efforts to introduce a standard format like Cloud Events but wondering if you guys have any different suggestions?

CloudEvents is trying to standardize on the messaging

https://cloudevents.io/

Hello guys, actually, vanus can directly deliver messages to OpenFaaS without this kind of connector. Because vanus can deliver messages that follow the CloudEvents standard, OpenFaaS can also receive such messages. More details https://docs.linkall.com/how-to/use-gcloud-functions

Unlike the other two connectors, the Facebook connector has been deprecated. Instead, it's now become an open-source project. So, you should use this open-sourced custom connector or something else. Fortunately IFTTT provides the Facebook Page connector, so you just use it.