I picked up Colorspace ZRO recently and it works just as I'd expect when measuring SDR. It's all manual (which is what I want actually) but easy to use and it's patch generator is easy to understand. Just set the symbol level of each color and there you go.

However, when I activate HDR mode, it still works as an SDR app, outputting SDR levels rather than HDR levels, even when set to ST2048 EOTF with a target luma of 10000 nits. It can measure brighter patches, if I fire up the VESA HDR Compliance Test software, but it doesn't seem to be able to generate them, which is a pain.

Is there an obvious setting I'm missing to tell it to output an HDR signal instead of SDR?

You need a compliant HDR TPG.

Steve

The most obvious to use is PGen, although for software only you can use Dogegen, or madTPG.
See the 'Addons' page of the LI website for Dogegen: https://lightillusion.com/addons.html
And here for PGen: https://lightillusion.com/pgenerator.html
While madTPG can do HDR, I've found it unreliable - but that may be me.

Sycraft
If you do go the PGenerator route, which is the most cost-effective hardware solution by far, you have to use a Raspberry Pi 4 or 400. No earlier Pi will do HDR, and the Pi 5 will not work at all.

I'll have to try Dogegen or madTPG because the test target is a laptop, so no input for a hardware solution like PGen.

The goal of this, of buying Colorspace in the first place, is to try and do some profiling of the display in the ASUS Strix SCAR laptop. It's a MiniLED display that is surprisingly bright and competent for a laptop, that is 100% complete garbage when it comes to HDR calibration.

I want to profile it and figure out what changing the brightness does to the EOTF precisely, and what brightness is the closest to correct (about 70 by my eyeballs) as well as get answers as to what it's ABL looks like, best settings to get proper colors in HDR without oversaturation (the default ICM file causes MASSIVE HDR oversaturation) and so on.

Not a normal use for this I'll grant you, and I'm not expecting any miracles, this isn't for color critical work I just want to answer the questions "What settings on this laptop makes it the least wrong?"

You will need a second monitor as an extended desktop to run ColourSpace GUI in SDR if you manage to enable HDR mode on your notebook's screen for the measurements.

If you're unable to enable HDR through TPG, you can utilize HDR media files and measure them manually using ColourSpace.