He has no "infinity" of anything. It's called leverage and it probably maxes out around 60-70% of everything he owns.
Musk has 100 billion of TSLA say.
He mortgages it to buy TWTR. Now he has 100 billion of TSLA, -40 billion loan against it, and 40 billion of TWTR. He could mortgage TWTR and buy something else, but it would have to be smaller, because the banks won't loan 100% of the value of the thing.
Or he'd have to make another $40 billion and pay off the first loan to mortgage it again.
Think of it as trying to use mortgage properties in monopoly to continue buying other properties.
Unless you're on robinhood: https://www.bnnbloomberg.ca/robinhood-traders-discover-glitc...
Maybe we'll see a wallstreetbets post "Musk couldn't take TWTR private but I did via robin hood bug"
By that logic though -- if you're a billionaire, could you try to buy every profitable company on borrowed money?
Eventually you'd make the money back and since you don't have to pay anything out of pocket, you effectively have $INFINITY dollars to bargain with.