The itch app uses a chromium browser under the hood. Similar to the steam app.
Games released for old system probably do a better job stating system requirements. New games would run in the browser, if exported as such, that's where the browser "test" comes from. I should specify that you need a modern browser, capable of html5 and all the bells and whistles. Or at least be capable to run such a browser at a practical and not a theoretical level.