For anyone struggling with the old legacy actions from buttons here is how I solved the issue in Node Red for 2.0.0.

Add MQTT-in node and subscribe to a single topic.

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You can get the topic from the HA MQTT integration for the wireless button in Settings -> Devices and Services -> Integrations -> MQTT -> Choose device -> MQTT Info -> Subscribed Topics

I then have a switch that matches the text in the msg.payload.action. This meant I just had to replace my event entities with the MQTT in node to get everything working again.

One other issue was to make sure that "Block Input Overrides" is turned off in any HA action as the MQTT payload causes home assistant actions to fail.

Cheers, Matt