• As a web developer: what a nightmare, now your website will look different to different people, as if having to support multiple browser engines and multiple screen rations, and multiple platforms, etc. was not a big pile of problems already.
• As someone who doesn’t like dark-mode due to eye strain: good-good… for people who like it ¯\_(ツ)_/¯
That's what the web has always been. People don't all have the same display types, the same subpixel layouts, the same display sizes, the same DPIs, the same fonts, the same zoom levels... People use reader modes, global restyling extensions, per-site custom style sheets, full screen magnifiers, bounded/partial magnifiers, screen readers, OS high-contrast modes... the web has never been a fixed canvas that you get to paint on and then hand to users.
(I say this as a designer who has spent countless hours on dark-mode palettes as well as someone who has the automatic circadian toggle enabled everywhere.)
> The HTML <meta name="color-scheme" content="light only"> tag lets browsers know that 1) this page supports light mode and 2) should only be displayed in light mode.