“You may deactivate your Threads profile at any time, but your Threads profile can only be deleted by deleting your Instagram account.”
Threads hit 10 million sign-ups in seven hours because Meta piped in Instagram’s 2 billion users. The exit got wired up the same way. Try Threads once and the only way out is to burn your Instagram account with it. Meta calls that a supplemental privacy policy. It is a hostage clause.