If cases are increasing everywhere because people spend more time indoors, as argued by the public health, why are cases increasing now in Texas where it is neither cold nor AC hot?

Because it has nothing (or very little) to do with people spending time indoors... (1/x)

Here is a study from March, showing a clear seasonal pattern. It shows that the virus prefers temperatures between 41-52 F (and no below freezing) and a very specific humidity. (2/x)
https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3550308

This explains why, despite likely circulating in January, the cases waited until March to explode. It was simply too cold for the virus to spread effectively. When the temperatures and humidity got right, it began spreading unchecked. (3/x)

From paper: "In the months of January 2020 in Wuhan and February 2020 in the other affected, there is a striking similarity in the measures of average temperature (5-11 C) and relative humidity (RH, 47-79%) (Table 1)." (4/x)

Cont.: "In addition to having similar average temperature, humidity, and latitude profiles, these locations also exhibit a commonality in that the timing of the outbreak coincides with a nadir in the yearly temperature cycle ..."(5/x).

Cont.: "In addition, none of the affected cities have minimum temperatures going below 0 C (Supplementary Figure 1)." Based on this, a few predictions: (6/x)

Current outbreak in the North (Chicago, etc.) should be short lived as the temps will soon begin to dip below freezing. Cases will soon begin to increase in lower latitudes as more places get inside the 41-52 F bracket. However, those places will too subside in the Winter. (7/x)

Despite what many claim, we will have low numbers throughout the Winter in most of the US (maybe except some of the South). However, in March, cases will begin increasing in the North again, but hopefully to a smaller extent because of population resistance and vaccine. (8/8)