It may have come off a bit snarky but it is the reality as far as the value of a high school diploma is concerned.
Completing A levels (or equivalent levels of high school education in other school systems) is not a professional qualification. What you learn in A-level anything is very basic and superficial compared with what you learn in an undergraduate degree, not only in terms of subject matter but also technical ability and experience accumulated along the way. So if an employer is looking to hire someone who already has relevant education or professional training it would make very little sense for them to ask for A levels.
This does not mean that somebody who has not got a university degree can only do a menial job. It merely means that it is entirely normal that employers are not going to post ads saying they want to hire someone with A levels, simply because that by itself is not a qualification of anything significant. Realistically, if the OP (or anyone in a similar situation) wants to do a professional STEM-related job then they are going to need significant training well beyond anything they learned in high school, and are going to have to think about how and where they get that training. University is one way (and probably still the most straightforward and worth considering; this COVID pandemic and the disruption it is causing are not going to last forever), but other kinds of professional training, certifications, internships, apprenticeships, or on-the-job training do exist.