Hardware Unboxed make some really excellent monitor reviews, and quite frankly, all HDR gaming is awful up to now.
See
Best 1440p Gaming Monitors of 2021, Plus Best Value Picks - 6th July 2021 - Hardware UnboxedJump to the HDR section
20:41 - Best 1440p HDR MonitorsWhich opens with, "if you're after a 1440p Gaming monitor with true HDR functionality, stop your search now because they don't exist".
The above, gives the PG329Q, the title of best 32" 1440p IPS Monitor, and the full review clearly states the HDR mode is not what you buy this monitor for.
Asus PG329Q Review, The Very Fast 32-Inch 1440p Gaming Monitor To Get - 19th Dec 2020 - Hardware Unb...The fact that the HDR Dimming was by design, is clearly pointed out in this FAQ
[LCD monitor] After using the HDR function for a while, the brightness of display will become darker...
Last Update : 2021/04/28, so it's not totally clear when this FAQ first said this, but at worst case it was, just 5 days after your post.
Frankly getting full HDR 1400 is not trivial, with high refresh rate Gaming monitors, and the very first to do HDR well, has took that long to develop, it is last gen tech on pretty much everything else, and with a $3,000 price tag it ian't cheap, but is 4k on a 32" IPS
Asus PG32UQX Review, Insane HDR Gaming at an Insane Price - 9 Jul 2021 - Hardware UnboxedIt's likely going to be another year, or two before true HDR 1400, can join other Gaming Monitor features, and tick all the boxes for under a $1,000.
I knew I wasn't getting a true HDR capable monitor, only one exists, and as with all first in class products, it comes with extreme price, and the usual early adopter teething problems, with the main one being it's extremely long development time.
But if HDR is what you want, this is the only Gaming monitor that gives you that.
I reviewed all the options, before settling on buying the PG329Q, on 9th of July, knowing full well I wasn't going to use the feeble HDR 600 mode for anything more than a look and see, before turning it off for good. Which I have done.