If you can't (or don't want to) install any extra app to your desktop OS, just open https://roundpie.app/ in your browser, log in, and start working.
There are some tips, though:
Pin the app's tab. Sometimes, a browser or some extension kills the tab in the background to save your computer resources (CPU and RAM). If the tab is killed, there is no way to continue ticking + there is no way to make sure the timer info will be successfully saved to the cloud log.
Remember that some hotkeys won't work in the browser if they can't be overwritten. For example, ⌘+S / CTRL+S (full sync) will work on the desktop app but not in the web app. The same is true about ⌘+R / CTRL+R (active project sync).
There is no way (at least for now) to define custom sounds in the web app.
There are plenty of handy tools like Rambox, Franz, and Shift where you can use the app if you care about your browser's tabs.