Another option you can also try:
Observe whether the audio peaks always correspond to the low frequencies (with the audio spectrum viewer (Shotcut-audio layout).
Then, if so, you can use the bass and treble filter. This filter has 3 frequency cuts (100 Hz - 1kHz - 10 kHz) and a good setting can make that -1 dB difference in the low frequencies.
This filter has no keyframe adjustment so the adjustment would affect the whole clip.
This filter has the advantage that you would lower the volume (you can also increase it) in one frequency range, while the other frequencies would remain unchanged.