I suspect he makes his money when his private company merges with the DWAC to go public (a SPAC deal). If that's correct, he profits on the merger, and not on the current stock price moves.
From a summary in Money Stuff, I suspect Trump can profit on both.
https://www.bloomberg.com/opinion/articles/2021-10-21/matt-levine-s-money-stuff-donald-trump-does-a-spacI think the official deal is structured as you say: Trump's underlying brand new company, Trump Media and Technology Corporation (TMTG), receives $293 million when it merges with DWAC, completing the SPAC deal. This provision is unaffected by DWAC's stock price as long as the deal goes through and no one redeems their SPAC shares; in this part of the deal, there's no direct upside to Trump from rising DWAC prices except that it encourages shareholders to leave their money in, ultimately guaranteeing TMTG gets all of the $293 million instead of part of it.
The terms envision that TMTG will use the $293 million to build social media that won't block people who get deplatformed elsewhere. If you assume Trump will keep most of the money and do nothing or create a low cost scam product and keep most of the money, then if you are right, he gets cash from the deal and whatever he can extract from the merged operation.
However, the deal also "values" TMTG with "an earnout of up to $825 million in shares (at the valuation they are granted)...depending on the performance of the stock price post-business combination." In a later Money Stuff article, I read that the main shareholders have a lockup period (can't sell shares too soon) and that the performance standard is that the post-DWAC share price needs to stay above $30/share. So Trump is highly incentivized to at least stoke enough enthusiasm to vest the extra shares.
If I read correctly, the SPAC deal will have current DWAC shareholders own 21% of the post-merger business (let's call it TMTG), but Trump still emerges from the deal owning 79% of TMTG outright if he wins the earnout. So the stock price matters a lot to him. I suspect he will hype the stock price regardless of how well the social network does (and the video service that they claim they might do).
As far as I can tell, nothing stops Trump from borrowing against his shares. If he can find a lender, he could borrow billions and still own 79% of the company. Pump up the price more, borrow more. Would lenders become more willing if he wins re-election and seizes undue control of the SEC and banking authorities?
To answer OP's question: Was definitely tempted to buy DWAC on opening day after reading the article (based on greater fool theory, not on any assumptions about "Truth Social" itself). Did not do it.