This App Records System Audio & Microphone Together in Ubuntu
Reco is a free, open-source audio recording app for Linux, written in Vala and GTK. Although it’s designed for elementary OS it works well on Ubuntu and other Linux distributions, and doesn’t look too conspicuous on the modern GNOME desktop, either.
Better still, Reco is available to install from Flathub.
Being able to capture your voice and your system’s audio output (be it game audio, software, music, someone talking in a broadcast) simultaneously is useful for content creation, be it conducting interviews to include in a podcast, making YouTube videos, or transcribing things for blog posts, etc.