I'm 100% sure this has been answered somewhere else on here within the last 2.5 years. (Edit: found the post I was looking for) TL;DR- increased turnout and more effective culture war wedge issue + urban-rural + educational attainment polarization.
I also thing there was a bit of the more social conservative Latinos voters voted when they normally wouldn’t due to the higher vote turn out all around. Thought that’s likely a smaller factor.
I don't think it's a small factor at all. The RGV swings can be explained almost entirely by extremely low-propensity voters waking up and turning out massively for Trump.
What people seem to be forgetting here is that 2020 wasn't a one-off. Despite 2016 being plagued by the border and immigration, the RGV swung and trended towards Trump that year. And despite Abbott winning statewide by a lesser margin than in 14' it swung in 18' towards him.
Even rural counties like Jim Wells, Duval, Starr, etc.. swung towards Cruz that year despite winning by 2 and a half point, other trended towards him as the state swung left. All that and Trump was nowhere near the ballot.
You didn't see that correlation between 2002-2004.
It should be noted that
GOP candidates didn't improve on Trump 2020 in the 2022 midterms like they did in South Florida.
