Can he spend, estimates, of his net worth ? Does he benefit if he doesn't increase the float and the stock drops from 80 to 20 ?

It doesn't matter. Trump knows that his share of DJT isn't really worth $4 billion. He can't actually sell it for that amount. DJT is a meme stock right now, and it only has value because Trump owns a majority share - and is therefore presumably 100% committed to it.

The question for Trump is how to maximize the benefit for himself. Increasing the float doesn't have any benefit to him - the stock's got plenty of volume, and generally increasing the float doesn't increase the share price. Selling shares would convert the "estimate" benefit to actual dollars, but there's a limit on how much he could actually liquidate without tanking the stock now. Meanwhile, though, he benefits politically by being provably a multi-billionaire - at least on paper.

What Trump should do is have DJT engage in the most profitable thing a meme stock can do. Sell more shares. People want to buy shares in a company that has less than $20 million per year in average revenue (and nothing but losses) at a valuation of close to $10 billion. The smart thing would be to have a secondary offering in a few months. Sell another 20-30 million in shares - small enough so that Trump still has majority control, but enough to make a ton of money off of gullible Trump fans and/or people seeking to curry favor with the candidate. That guarantees Trump a several hundred million dollar payout at the end of wherever this goes, without tanking the price any more than would happen 'organically.'