In my opinion, Network Speed Test is one of the best internet speed test apps for Windows 11/10. It is an app from Microsoft Research and provides accurate results. Plus, it even lets you know what you are capable of doing with your current internet connection. Besides this app, Speedtest by Ookla is also an accurate and good internet speed test app for Windows 11/10. You can even export the internet speed test results in this app. Plus, there is a web version of this app which is quite popular for testing your internet speed. You can also try it to quickly determine your internet speed.