Hi, welcome to the forum!
When the Fairphone 3 was released it had a bug that applied a kind of noise reduction filter to videos recorded with the default camera app. At that time I recorded a video to show it, in which I compared the original recording with a recording made with the Open Camera application (F-Droid or Play Store) and with two different settings. You can watch it here:
I haven’t used Open Camera for a while, but I think you might find it useful for recording live music concerts by selecting the “Audio source: unprocessed” option. I imagine that setting selects the lowest possible gain that the microphone picks up.
I hope that helps.
Best regards!