Unfortunately, the myth that virii become weaker over time is a long standing misconception, and the anti-vax people pushed it because it fit their narrative.

These articles discuss it with immunologists & doctors & geneticists, though, so it seems that it’s a known truth and so, like gravity, isn’t extensively studied. Instead, they’re focusing on actual prevention via better vaccines and personal behavior/responsibility.

Hope this helps!

Https://www.npr.org/sections/goatsandsoda/2022/01/14/1072504127/fact-check-the-theory-that-sars-cov-2-is-becoming-milder

https://abc7ny.com/covid-update-pandemic-do-viruses-get-weaker-as-they-evolve-omicron-variant/11463220/

https://www.businessinsider.com/coronavirus-not-mutating-to-be-weaker-over-time-genetics-2020-7

https://en.as.com/en/2022/02/07/latest_news/1644263846_400285.html (note that this site is a Spanish-language sports site, but it was nice to find this there)