It still depends on the target audience. Some websites or apps are single-page applications (SPAs), can older devices handle that? For example, my mum’s Android phone was too slow to even load a page.
Secondly, users should upgrade their devices to stay safe online, since vulnerabile people are often scammed or tricked into downloading apps that contain malware.
So we should not cater to outdated browsers when they could pose a risk.
Yeah, I'm very amenable to this take. WordPress, for example, is infamous for having extreme backwards compatibility. But that often results in many sites being on ancient versions of php (and surely other tech as well). I'm of the opinion that they should all be running currently-supported versions of php and everything else. If you can't use my plugin because your server is shit, so be it.
This time, iOS 26 adds the ability to create a shortcut to the Home Screen as a web app, which definitely needs a dark mode. It appears that none of the extensions are loaded