Texas is not going to secede. In the 2020 election, the vote was 52:46 between Trump and Biden, meaning almost half the state supported the overall national winner. Compare this to the actual secession crisis election in 1860, where the vote was 75:24 against the pro-Union candidate, with Lincoln not even on the ballot in the state.
"Third. New States, of convenient size, not exceeding four in number, in addition to said State of Texas, and having sufficient population, may hereafter, by the consent of said State, be formed out of the territory thereof, which shall be entitled to admission under the provisions of the federal constitution. "
(This is Texas trivia for mutual amusement, not a serious suggestion.)
What was annexed and what is now Texas are not the same thing. Some of the area of the original Texas already is part of different states (no other state is a majority of old Texas though)
With the caveat that I know very little about the legal aspects surrounding secession, Lawrence Wright in his book "God Save Texas" mentions that the idea of secession is only a talking point and it's not going to happen legally.
I feel like articles like this is mentally preparing the American public for a potential secession states forming post-election.