First, I am surprised he was not previously on the list of Richest 500. With the global wealth explosion, I can imagine he had moved off of it.
Second, the $3 billion increase in net worth is all paper. Until he sells that stock, it really means nothing but bragging rights.
Few people, billionaires or otherwise, keep their wealth in cash. Stock is a liquid asset BTW.
That said, there is a 6 month post merger lock-up agreement in place during which shareholders of TMTG who own more than 10% of stock are not allowed to sell or exchange.