The perception is probably a misinterpretation of the uncertain future prospects for the middle class. The economy is becoming more unequal and less meritocratic, with the likely result that the middle class will shrink, with more of the current middle class and their kids being downwardly mobile than upwardly mobile. With a “shrinking pie”, people tend to become meaner and look for additional ways to exclude competition for their jobs or economic class position (including by race, ethnicity, religion, etc.).
Note also that middle class anxiety about uncertain future economic prospects is also fed by the apparent faster pace of change in labor markets, sometimes faster than humans can adapt and retrain to new jobs that get created as old jobs become obsolete. Also, new jobs may be in different regions, while some people may have other constraints (e.g. spouse/family) that limit their ability to move to different regions (there is a recent thread about someone considering moving for the spouse’s job, but which would result in a less desirable situation for the high school student’s college prospects). A coal miner in West Virginia looking at declining coal demand and impending closure of the mine and/or automation replacement of labor at the mine might not be comforted by the availability of jobs building and installing solar panels in the sun belt, or building and installing wind turbines in the plains.
The pace that humans can adapt and retrain to new jobs is also slowed down by increasing credentialism and professional licensing requirements for many jobs. Jobs that used not to require a bachelor’s degree now often specify that as an initial screening, even if no general skills indicated by a bachelor’s degree nor major-specific skills are needed for the job. Of course, education and training is now more expensive, and more likely to be born by the individual, rather than subsidized by the employer or done on the job. In other words, the barriers to retraining for new jobs are higher now than before, contributing to middle class anxiety.
I do see US-born software developers younger than 40 (including white and non-white ones), but they do have a tendency to move to smaller startup environments more than others (probably because some of the non-US-born are on work visas and find it more difficult to change jobs or get visa support from startups).
However, one thing I did notice decades ago was that white students in engineering tended to have a higher attrition rate than other students, so that the percentage of white students at the engineering graduation was oddly low compared to the percentage of white students in the frosh level courses for engineering majors (or the school overall). This was at a school with direct admission to engineering majors and a 2.0 college GPA requirement to continue, so it was not one which actively weeded out students after enrollment (unlike some schools where enrolled students start in pre-engineering and have to compete by college GPA to get into their majors).
More recently, I attended an engineering graduation and noticed the same relative lack of white engineering students graduating. Although it is true that overall demographics of the state and the state university have become less white over the decades, the small number at the engineering graduation was still greatly underrepresented compared to what one might expect compared to demographics of college frosh.
So perhaps the lack of young white people in engineering and computing may have something to do with where they are earlier in the pipeline. (It probably does not help that some flagship universities in states with higher white populations practice deliberate weeding in their engineering programs.)