Exciting us the most with Chrome 90 is AV1 encode support now in place with the main use-case being for WebRTC usage. Chrome is making use of the reference libaom encoder for CPU-based AV1 encoding and with powerful enough hardware can be used for real-time video conferencing.
Chrome 90 also has a number of new developer APIs, continued WebXR work, CSS aspect-ratio interpolation, custom state pseudo classes, "overflow: clip" CSS support, WebAssembly exception handling, and other additions.
The list of security fixes for Chrome 90 can be found via the Chrome release blog . A lengthy look at the developer and user changes for Chrome 90 can be found via ChromeStatus.com .