In Soviet economy virtually all people had a job though. In communist Poland where I grew, safe for the years of martial law in mid 80s everyone who wanted a job had one.
New businesses will form. Why wouldn't they? We have a ton of businesses that even 50 years ago no one would imagine. We can continue up the pyramid to more and more things that wouldn’t be possible or practical today.
Your mistake is you’re looking at a future world in todays state.
Why would they? There is nothing suggesting that there are infinite industries to be invented, once we have automated our core industries, will we all be working for superfluous industries? Seems far more naive to assume the status quo of total employment will continue due to some unforseen future of yet known new jobs, rather than thinking criticaly about the more near future outcomes of a much deeper automation of jobs we already have.