For casual testing, you can simply use https://openspeedtest.com. This lightweight tool runs on a tiny Nginx server, eliminating the need for additional software installation. It effectively handles network speeds up to 2-3 Gbps on most systems from 2014 or newer, reaching 10 Gbps+ for those built in 2019 or later. M1 Mac Minis and newer systems can even achieve 20 Gbps+ speeds. However, for requirements exceeding 20 Gbps, a browser-based test like OpenSpeedTest might not be the most suitable option. The good news is, it can cover most of use cases without requiring any additional software on the client device. Just utilize your web browser! For maximum performance, however, avoid Firefox and opt for Chrome, Edge, or other Chromium browsers.
OpenSpeedTest Github :: https://github.com/openspeedtest/Speed-Test%C2%A0
OpenSpeedTest Docker :: https://hub.docker.com/r/openspeedtest/latest
OpenSpeedTest-Server is available Microsoft Store, Apple App Store etc. :: https://go.openspeedtest.com/Server