As far as I understand, Fetch API is supported but I couldn't make it working.

On the code like fetch(request)... I got an error ReferenceError: "fetch" is not defined.
On the code like window.fetch(request) it fails with TypeError: Cannot find function fetch in object [object Window]

I use 2.36.0 version with htmlunit-driver and RobotFramework. The code for creating htmlunit driver is the following:

https://github.com/Hi-Fi/robotframework-seleniumlibrary-java/blob/fed6f0e95b5cf5a365f8357a9976ec9ed7ff7e1e/src/main/java/com/github/markusbernhardt/seleniumlibrary/keywords/BrowserManagement.java#L782-L785

I expect that it will use default browser that is CHROME and it should have a support for Fetch API.