He can’t sell until September 19, during which time the stock will go lower yet. And once he starts selling it will go even lower, and even lower, and he won’t be able to help himself from cashing out as much as he can as quickly as he can, which will tank it even more.

I wonder if it's worth it for him to try to sell very much, if any.

The "value" of DJT is Trump's usage of Truth Social and ownership of the stock. Trump isn't contractually committed to using Truth Social (and he's started to use X again), so the only thing that keeps him using it is probably his ownership of the platform. And the only reason any third party would ever advertise on Truth is to curry favor with Trump. So DJT only really has value as long as Trump is the majority owner of the company.

If he started selling, he probably wouldn't be able to sell more than a handful of shares at the current market price. If he tried to move towards exiting his position, the share price would collapse precipitously. While on paper the value of his shares is north of $2 billion, there don't exist buyers that collectively would give him $2 billion for his share of the company.

He's probably better off just keeping his illusory wealth illusory, but intact, for as long as he can. Sure, maybe sell a few percent of the company at north of ~$15 per share to get a little money off the table, but stop at that.