I do, with a passion!!
I'm a sports photographer and remove my cards 10-20 times during a football match and need to do this one-handed. It's near impossible especially if I have wet or sweaty hands. The door is such a letdown compared to the D5. I'm hoping someone at Nikon takes this seriously.
Z9 door opening technique, their is very easy quick way to open the door one handed.
I find the door to be in need of better instruction technique from Nikon rather than in need of a redesign.
I can understand your frustration as a sports action shooter, while the door opening is perfectly fine and very easy for me normally, being on a mono pod like you use and having one hand only and needing to open the door quickly as often as you do, i can see that its an issue and a frustration, this prompted me to have a quick look.
When i simulate your position, yes, it is an issue initially till i looked further, i mean if speed is required. I mean i found it doable and tolerable just slow and very uncomfortable and would vary if it was cold or hot.
So while not impossible i do think in your situation its well noted and in need for Nikon to refine the door opening system possibly be it better instructions advising of the correct technique rather than look at a redesign, after all its a professional sports action wild life camera.
That said and here is the twist.........
I can see the need for the door to have integrity, heat and cold can cause condensation, these cards doing a lot of video will get much hotter than usual.
Also given the high level of performance and specs of the cards and camera electronics water or condensation dust or dirt could prove fatal,
so i think the door seal integrity is more important than ever.
So i looked a little closer........
When i look under the door and felt the edge of the seal area on the camera it seems to have a fine rubber like seal, when the door is closed their needs to be a downward pressure on that rubber like seal to make the seal complete.
I found that the door closing on a rubber like seal needed pressure to close and surprisingly downward pressure to open.
If i take my two fingers pointer first slide the button down then with both fingers press the door downward onto the seal and with both fingers slide the door forward, ie: its a two finger operation, the door is very easy to open one handed. I found pressing the door down onto the seal to the ease of the door catch releasing worked so well, the downward pressure actually compresses the rubber seal under the flap, the door fly's open one handed.
Ok simulation take 2, LOL,
With a bit of practice it got so simple.
I then asked my girlfriend to do the similar thing, initially it was hard, once she got the hang of it she found it easy fast and workable.
Recommendation its a two finger application pressing the door down into the camera seal to release the pressure of the catch works a treat.
So now i use two fingers press the door and with both fingers slide it open easily.
I find the door to be in need of better instruction technique from Nikon rather than in need of a redesign.
I feel if the knob on the door you slide is made a little more proud so you can easily get a stronger purchase on it, that would go a long way in the right direction.
I loved my door on the D3X, push a button the flap would open, easy as.
Only an opinion