External display will not achieve full brightness?

My external display (HP 27f 4k ) will not achieve full brightness when connected to my M1 MacBook Pro (2020, 13", Ventura 13.2) via the official Apple USB-C HDMI adapter . - The display's brightness is cranked all the way up - "*True Tone*" is off - "*Automatically adjust brightness*" is off - "*Slightly dim display on battery*" is off - I've recalibrated the display color, gamma, and white point (in macOS) and then restored it back to the factory default (because it made no difference to the brightness) I noticed this because I sometimes need to use a Windows laptop with this display. The monitor on Windows was noticeably brighter. So, I measured the brightness with a screen calibration tool and compared the results of the same monitor in the same location (all the same external variables) with the monitor plugged into my MacBook and then into a Windows laptop. I measured against a fullscreen browser window displaying a page with nothing but #FFFFFF (white) as the background color. Results: - 290 nits from the MacBook - 335 nits from the Windows laptop What's going on here? I suspect this is a software thing because I *think* I've seen the display snap from full brightness to this dimmed state after login. I say "think" because now that I've decided to write this post, I can't reproduce it. But my memory is that I'll log in, and seconds after the desktop is displayed, the brightness snaps to this dimmed state.