Your device night mode is not compatible with those apps..they have their separate dark mode option..and this is not an issue.. For chrome, you can enable dark mode- paste this in the address bar 👇 chrome://flags/#enable-android-night-mode
Once entered, they would come across an option in the dropdown menu called ‘Android Chrome UI dark mode.
Tap on ‘Enabled’ and relaunch the browser. For youtube: Go to general settings and enable dark theme.