True if Trump starts posting to Twitter, AND that return is later claimed to have been due to a security mishap such as stolen device, password guess, misbehaving staff, malicious interference with network or staff, or similar.

If Trump starts posting on twitter, then claims those posts were hacked/illegitimate/etc (as above), it's true. But if he only claims some later posts were illegitimate, but his initial returning posts were legitimate, the market resolves false.

Update 8/3/2023: This applies to twitter or whatever it becomes, any entity which is the home for all past tweets and is a continuation of where they were posted before, should be considered to be true twitter regardless of name changes / format changes etc.