A special election is more of a short term indicator rather than a long term one. Turnout is usually pretty low compared to general elections and unless there is hot button issue at the time, the predominant party's base typically turns out in higher numbers. The long term trend of this particular district is that it is trending Democratic. Bush won this district with around 65% of the vote. Trump won it with 54% in 2016 and only 51% in 2020. Case and point, Scott Brown won the Senate seat in the Massachusetts special election in 2010 because even in deep blue Massachusetts ObamaCare was a touchy subject. However, he failed to get elected to his own full term in 2012 and the state is no less Democratic today than it was ten years ago.
Long term, Texas is turning Democratic, but Trump did appear to provide a blueprint to reverse that. If the Republican Party was smart (don't hold your breath) they would study what parts of Trump's agenda appealed to minority voters that got more of them to vote for him than past Republican candidates. Trump managed to get Hispanic border counties to vote for him overwhelmingly that haven't voted Republican in 100 years and went handily to Clinton just four years earlier. That's what Republicans need to be looking at and the key to holding on to the state. They probably won't do it, though, because the Republican Party is useless.