In laptop with Realtek system, the Wasapi/Realtek loopback recording has the basses cut off.
The solution was to plug in earphones (or external speakers).
If I guess correctly, the laptop speakers are protected from excessive basses. That is ok, but then the loopback point should be before the protection filters.
By the way, OBS does not have this problem, because it can record directly from the application (Firefox). Maybe Audacity should have something similar to what OBS has.