Anything that uses the electron framework uses chromium.

Although in the case of steam they are using the Chromium Embedded Framework(CEF) to embed the steam store into their interface, as well as to power the steam overlays browser.

The worst part is, the CEF really is the only way to implement browsers inside other interfaces. OBS uses it too for it's browser source. There really isn't any alternatives - if only FF could create it's own Firefox Embedded Framework to compete, but that's probably not in the cards due to costs. Mozilla is a not for profit relying on donations and grants.

And electron is a method for creating desktop app interfaces using website code, it's used for the interfaces of Discord, slack, teams, Streamlabs (yeah they ripped out the OBS Qt interface and replaced it with electron), and sooo many other modern applications that it's hard to make track of. And it uses essentially the same thing as CEF at its heart.

Basically any website can be wrapped in an electron wrapper to produce a standalone desktop app.