So far as I understand, there is a common idea that Texas has the legal ability to leave it it wants, but it’s just a popular myth as far as I’m aware. Whatever their state constitution says doesn’t matter anyway, because federal law trumps state laws and as far as I’m know there’s not a legal mechanism for states to leave again, it’d have to either get the government as a whole to make legal or possibly even constitutional changes to allow it, or leave illegally, either by force or by having a sympathetic government just not press the matter and just ignore the laws in question. I can’t really see them getting enough support for the former two, they’re too weak compared to the federal government for an actual war, and the current administration is not likely to just let them go, so I don’t expect them to go anywhere unless one of those things drastically changes.