Sound output through monitor on Mac too loud and unadjustable I just got a 2020 i3 MacBook Air and have an adaptor to connect it to my monitor over HDMI port (which I plug my headphones into) but when I try to listen to anything the sound is way too loud. I've tried going to display and changing the volume but the slider does not work (it is fixed at the top).
The monitor is a Dell HDMI monitor. The sound is unusable like this. What can I do?
You can use a 3rd party utility called SoundSource which lets you control the volume of the external display connected to your Mac using the Macs built-in volume controls.
SoundSource is a macOS app from Rogue Amoeba, a well known and reputed developer of audio utilities for macOS.
While SoundSource is a paid app, Rogue Amoeba provides a fully functional but time-limited demo of the app which you can try to see if that resolves your issue.

P.S.: No affiliation whatsoever with Rogue Amoeba or any affiliates. I have been using SoundSource on my personal Macs and I am highly satisfied with it.