Don't you have a light/nits-meter, then you could get some tangible numbers that other people could replicate as I would guess many do have light-meters, as they are quite cheap and even the budget ones, perform quite decent.
Should be possible to dim the room, and create a lid scenario on the scope in the circumstances where you sense that its "dim", that other owners can replicate, and compare values -
To conclude if the unit's display is underperforming, as brightness/dim is relative, varies from one to the next..
Was unsure if it's a TFT or IPS in DHO8/900 series but from the looks of videos on the DHO800-900 series and the glow from certain angles, I would guess it's an LCD TFT display, which is quite common on scopes.
Checked the max brightness on Micsig-STO-scopes which peak at 414 on battery with just a white slide as light-sample, haven't tested fx a wide waveform to see what it musters in the scope app, but it's bright enough that it's fully useable outdoors, & indoors needs to be dimmed down quite a bit for my taste..
the scopes topglass screen also seems to be frosted like you see on fx mat or anti.glare screens. even though it's a glossy touchscreen.
- An example of the frosted native glassscreen & the LCD TFT RGB grid -
https://tinyurl.com/nw958xat - three first pic is the same and vice versa for the two last, only the focal depth varies, - that glass-frosting also makes it difficult to get the pixels into focus...
Tried briefly a few years back to put a screen-protector on the Micsigs screen, to see what amount it would counter FX glare, but it made it hazy from the TFT light glow underneath clashing, as I doubt it is laminated, so that was a clear no-go for my taste and peeled of again.. - it undermined some of the dark contrast that I personally prioritize a lot, as I prefer the waveform-background to be as close to inky black as possible.
Likely also why many scope vendors pursue TFT vs IPS, as IPS has a tendency to undermine the dark in the infamous IPS-hazy-glow (light bleed) that partly tones black into grey'ish...though, it is getting better for higher-end IPS panels.
An OS brightness slider hopefully will see daylight in future FW.