Add "Window Controls Overlay" overall support, window-controls-overlay option for display_override in the web app manifest, the -webkit-app-region/app-region CSS properties, the relevant CSS env vars (titlebar-area-x, titlebar-area-y, titlebar-area-width, titlebar-area-height), and the JavaScript API (navigator.windowControlsOverlay).

Currently behind flags, origin trials, etc.
Chrome is planning to ship in Chrome 98, according to Chrome Status (see link below).
Available behind the #enable-desktop-pwas-window-controls-overlay flag in Chromium-based browsers since at latest v93, by the Microsoft docs.

Not sure if it should be added yet, but would be useful to have it available so that people like me could have found the support status easily without having to do their own research. There have been other features added that were/are not supported at all.

Relevant links:

• Customize the window controls overlay of your PWA's title bar - web.dev
  • Support status
• Chromium issue - bugs.chromium.org
• Feature: Window Controls Overlay for Installed Desktop Web Apps - Chrome Platform Status
• Microsoft docs how-to - docs.microsoft.com