Microsoft has announced that web apps will now be able to use Protocol Handlers in Microsoft Edge, starting with Microsoft Edge 96. The latest feature will allow installed web applications (or PWA) to navigate pre-set or custom protocols. Installed web applications will also be able to register with the operating system as protocol handlers and initiate once a particular protocol is invoked.
In case your web app has the capability to register as protocol handlers, it will have "better integration with the operating system, and can be set to open specific protocols". It can also be set as a default handler, which means that if you are developing a web app that is an email client, you can provide the users with the option for it to be the default application for generating new emails.
Moreover, you can produce custom schemes that your web app can manage by registering protocols that are prefixed with web+. It can act as a helpful resource in case you need to navigate a URL for which "the set of safelisted schemes doesn't fit the bill."
In order to register your installed web application as a protocol handler, you need to employ the protocol_handlers field in the manifest file. If the protocol-handlers field is available in the manifest, in that case, the web app will be registered as a protocol handler for the protocols defined in the collection, during installation.
Protocol Handlers offer support for Windows, Linux, and Mac. The blog post mentions that Microsoft has "contributed this work to the Chromium open-source project" and the feature is available in other Chromium-based browsers as well.