Yes, it is possible to simultaneously record audio while capturing or recording video in the target app.
Web Browser Version
While capturing video, you can record system audio (※) as well as microphone audio such as narration.
※ Only when a browser tab is selected as the capture area
▼Capture images and video and add steps (Web Browser)
https://teachme.jp/8/manuals/35657034
Mobile App
Since audio is recorded simultaneously during video recording, you can create a video with audio by narrating while recording.
▼Upload video (Mobile App)
https://teachme.jp/8/manuals/7899343
If you want to add audio to an already recorded video at a later time
Teachme Biz does not have a feature to add narration to videos.
Please consider using standard applications on Windows or Mac, or online meeting tools to add narration.
▼How to add narration to a video (Windows, Mac)
https://teachme.jp/8/manuals/30427690