If you want to record system audio and can't find Realtake Output in the Monosnap video settings, please try to update Realtake HD Audio Drivers:
1️⃣ Press Windows Key + R then type devmgmt.msc and hit Enter to open Device Manager.
2️⃣ Expand “Sound, video and game controllers” then right-click on Realtek High Definition Audio and select Update Driver.
3️⃣ On the next screen click on “Search automatically for updated driver software“.
4️⃣ Wait for the process to finish finding the latest available update for your sound drivers.
5️⃣ Click on Install to complete.
6️⃣ Click Close and reboot your PC to save changes.
7️⃣ Launch Monosnap.
8️⃣ Go to Settings > Video.
9️⃣ Set up Audio output: Realtek Digital Output.