This may be an unpopular opinion but there won't be a Twitter replacement. There may very well be a "next big thing" but it won't be like Twitter the same way Twitter wasn't like MySpace or MySpace wasn't like FARK etc (not to say these are in any way directly related but Twitter certainly wasn't the biggest social network by far even if it was culturally influential).
Mastodon exists and it is good at being a federated microblogging service. Threads exists and it is good at the metrics it's built to deliver. Bluesky exists and it is good at being its own little club house. Truth Social exists and it is good at being Trump's soapbox. Gab exists and it is good at being whatever it is.
Twitter hit a magic sweet spot that can't be replicated. It was also a terrible place even before the cultural shifts (including those prior to the leveraged buyout). It was the place celebrities would show their entire ass to journalists and everyone could tag along to tell them how terrible they were. It was also the most readily accessible source for "citizen journalism" with unfiltered live coverage of major tragedies and other "breaking news" - but this has now become impossible as it has also become easily accessible to spread falsehoods that overwhelm any attempt at fact checking.
X's "revenue sharing" mechanism that effectively monetizes outrage bait may be what's killing Twitter for good but even prior to that Twitter was already dead. Heck, Twitter was always bad even when it was useful. At times the up sides just outweighed the down sides if you knew how to use it. For many this involved "not being political" (which is already not an option if your identity deviates from the "norm" in obvious ways, e.g. being a woman) and sticking to specific niches. But the discoverability of these niches is also what made them prone to the inevitable Twitter drama.