The rise of next-generation social media platforms-such as Truth Social, Bluesky, and Mastodon-has introduced new dynamics to online political discourse. Characterized by decentralized governance, ideological alignment, and alternative moderation models, these platforms have become key arenas for fragmented political expression in the post-Twitter era. This study examines how factual political content is framed and engaged with across these platforms, focusing on discussions around Donald Trump and Joe Biden during June 2024, a month marked by high-profile legal and electoral events. Using framing theory and a multi-method approach-including semantic similarity modeling (SBERT), network analysis, and large language model (LLM) classification-we reveal stark differences in narrative construction and user engagement. Truth Social exhibits cohesive, conspiratorial framing and strong narrative reinforcement; Bluesky reflects ironic detachment and a diversity of stances; Mastodon emphasizes civic critique within lower-volume but thoughtful exchanges. Despite engaging with the same events, these next-gen platforms cultivate distinct discursive ecosystems shaped by their infrastructures, norms, and user ideologies. Our findings highlight how emerging social media alternatives are not simply replacements for legacy platforms but are actively reshaping the contours of political polarization and public debate in the digital age.

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