To try out the PiP feature, you need to use Microsoft Edge based on Chromium, and then you need to visit YouTube. Open a video there, right-click it and select Picture-in-Picture mode.
Of course, it goes without saying that downloading and installing applications from unknown sources can be risky. That is, if you want to try the leaked version of Microsoft Edge, you can install itvirtual machineIt's safer.
On the other hand, Mozilla is working hard to bring Picture in Picture mode into Firefox browser, so you can download a Nightly version for testing.