All - just in case there are still others in the group working with the SDK but suffering from the thin documentation and limited samples, I've been experimenting with ChatGPT to write me code samples of the Apex handlers. So far, so good. It sometimes defaults to writing against the Slack API, but you just need to gently remind it that you want code using the Apex SDK classes.  An example - 

I prompted: "When using the Apex SDK for Slack (Beta), write me an Action Dispatcher class that when called from a message view in a users channel, it will update the original message in their feed when invoked."

When it came back with API code, I simply nudged it..."Instead of coding to the Slack API, please use the Apex Slack SDK classes to do the same thing."  - and it did.

Give it a try and lemme know.