In the "let them eat cake" scenario, those people will have plenty of free time to stage a revolution and take their piece of the cake by force. Below the threshold of civil war, you get a Wild West where armed bandits hold up trains of self-driving trucks and loot them, creating a thriving job market for security guards protecting the trucks.

Of course both of those scenarios are highly undesirable, so it's more likely that some kind of tax will be introduced to take automating jobs from extremely profitable to barely profitable, with the proceeds used to pay for unemployment benefits and retraining for the displaced workers. (With the amount of retraining depending on how many other jobs haven't been automated yet.)

That said, some people are going to see their standard of living decrease without any way to escape. Such people have existed since forever, and they usually end up homeless if not dead. Automation doesn't create any new problems in that regard, it just makes them large enough that they can no longer be ignored easily.

I can only imagine what you’d write at the time when first cars came to be or combustion engine ...

Your position is evidence for the power of propaganda.