Donald Trump left office on January 20, 2021 and subsequently created a new media enterprise, Trump Media & Technology Group (TMTG), which owns the social media platform Truth Social. Truth Social was announced in October 2021 and publicly launched in February 2022; it is explicitly described as a social networking service founded by Trump and owned by his media company, which has since expanded into other media/streaming and related ventures. (en.wikipedia.org)

After leaving office, Trump also actively tried to act as a political kingmaker in the Republican Party:

• He issued a large number of endorsements in GOP primaries, and coverage of the May 2022 Ohio and Indiana primaries described them as the first big test of his status as the Republican Party “kingmaker” — a test that Associated Press analysis said he “passed” when his endorsed candidate J.D. Vance won the Ohio Senate primary. (wsls.com)
• Political reporting repeatedly framed him as a “kingmaker,” noting that Republican candidates in places like Arizona actively sought his backing and that Trump used rallies and endorsements to shape primary fields. (rollcall.com)
• His endorsements were pivotal in unseating several House Republicans who voted to impeach him in 2021, demonstrating his deliberate effort to reward loyalists and punish opponents inside the party. (en.wikipedia.org)

While commentators debated how effective he was as a kingmaker — some arguing he was less decisive than advertised (theguardian.com) — the prediction only claimed that he would launch a media business and try to become a GOP kingmaker. Both clearly occurred, so the prediction is right.