The fastest Ubuntu edition is always the server version, but if you want a GUI take a look at Lubuntu. Lubuntu is a light weight version of Ubuntu. It’s made to be a faster than Ubuntu.

Why is Ubuntu 20.04 so slow?

If you have Intel CPU and are using regular Ubuntu (Gnome) and want a user-friendly way to check CPU speed and adjust it, and even set it to auto-scale based on being plugged vs battery, try CPU Power Manager. If you use KDE try Intel P-state and CPUFreq Manager.

Is Ubuntu 20.04 LTS stable?

Ubuntu 20.04 (Focal Fossa) feels stable, cohesive, and familiar, which is not surprising given the changes since the 18.04 release, such as the move to to newer versions of the Linux Kernel and Gnome. As a result, the user interface looks excellent and feels smoother in operation than the previous LTS version.