Yes this shift to React is really annoying. Github also stopped working on older browsers.

My leisure laptop is an older macbook with firefox 78.15.0esr and a little over a year ago I stopped being able to view github files and issue discussions with it. I can still view READMEs most of the time but now I have to use chromium or another computer to actually read code without cloning the repo.

I know they could easily generate JS for older browsers if they cared to set the esbuild target.

Pretty much all of Microsoft — Admin Center, Entra, Defender, etc, they all load slowly and then show you more "silver shimmers effects".