Quick Look in Finder always resets volume to max — super annoying for editors

This is not new behavior, QuickLook starts at max volume by default. The only difference is that it's right in your face now.

On Sequoia (and from what I recall, prior versions of macOS), there was just a volume icon in QuickLook

You had to hover over it to see that it was at max volume.

Adjusting it down applied to that ongoing preview, but if you closed the preview and reopened it or opened another file, it was back to max.

In Tahoe, that slider is just right on top so you notice it, no hover-over required.

Only Apple can change this. To have Apple consider your feedback, submit it here:

Feedback - macOS - Apple

Update to 26.1 and test again.

If you mean the volume slider that appears in QuickLook, yes, it is set to the max all the time:

If you mean the general volume control, no, or at least I cannot reproduce it.

It seems to me that all you have to do is set the general volume to an acceptable level, either from the menu bar, control center, or the media keys on the keyboard.

I misunderstood your question. I thought you meant Quick Look changed the volume of the computer every time. As the others explained, Quick Look volume level always opens maximized. Feel free to send Apple feedback.

I don't know what would cause the issue. It doesn't happen on my Macs running Tahoe. Do you have any audio enhancement software installed?