Using the latest Stellarmate OS and Android app on Samsung Tablet S6 Lite (WiFi only, no magnetic sensor)
It has some minor quirks to get used to, but as a veteran Linux power user, nothing too bad to abandon Stellarmate.
1. I went through the video tutorial to try out the Polar Alignment Assistant. Auto routine works like a charm using 600x mount speed, but when it comes to zooming in/out and panning the image to a bright star and adjust the correction rectangle, i actually can't do any of these actions, neither in minimized nor fullscreen display of the periodicallly captured/refreshed image.
2. As an alternative, can i just switch to VNC/Kstars->Ekos and do the PA there, continue with Stellarmate app afterwards?
3. As the VNC connection is rather slow, would it make sense to use an external WiFi Dongle+Antenna instead of the RPi4 internal one?
Another workaround (at home) would be to connect via VNC over Ethernet Powerline, connected to my WiFi home router. I could then even use INDI compatible clients to connect to the RPi4. When i'm out in the field i would be limited to WiFi-Hotspot mode, of course.
Answering parts of your question (I don't use the stellarmate app):
I do what you suggest at home (powerline networking and VNC--really NoMachine) and it works fine. I actually connect a switch to the powerline so I can plug in a laptop outside near the telescope, should I need to (my home WiFi does't reach my home telescope's location), but I primarily access the scope using NoMachine across the network from inside my house via the powerline network.
I would think you should be able to polar align your scope outside with the standard linux-based KStars/Ekos program, then disconnect the laptop-based KStars/Ekos and reconnect to the app. As I said, I have no experience with the app, but I would expect that to be fine.
I'm going to try platesolve PA, as i had this on my mind lately, but i hope platesolving around Polaris will work on a 430mm APO with an APSC type CCD behind it, because i am not (yet) using a guidescope with a wider field of view to feed more nearby stars to the platesolving algorithms.
I'll post back here how it worked, but it will take some time, because i'm away for the next two weeks and the skies are likely to be cloudy until i am leaving.
Regarding StellarMate App PAA, using two-fingers gestures to zoom in and out definitely works and so does tapping around. You'll see sometimes couple of seconds delay since the image is not local but getting transferred every time you click around.
If you're handy with a scalpel and a soldering iron, you can add an external antenna connector to your raspberry pi. It's not super difficult, but you do have to solder a few very small components (between 0.1 and 0.5mm in length).
If you (quite rightly) think that sounds like too much trouble, you can get some sort of external wifi extender. ASI Air users report good results with Vonets wifi bridges (which work well for my TV and my oscilloscope so I'm sure they'd work with stellarmate), or you could use a travel router in repeater mode (which does work well).
I can see a little yellow circle at the beginning of the triangle, which is moving a slight bit (a few pixels) one to two seconds after each finger action in the image. I will try some other things, like using different Android devices. Maybe the problem is specific to my tablet.
I'm quite skilled regarding electronics, but in this case i will try the convenient way of using a Linux "compatible" USB-WiFi dongle with a better antenna and at least capable of 802.11n mode.
EDIT: quoted text seems to be stripped in standard view. The second paragraph was a reply to Chris Kuethe's post.
To further add to this; I gave up on external wifi adapters (I kept breaking the antennae) and switched to a mini-router that sits on my tripod. I just run an ethernet cable down to it and it acts as an extender to my main network and still runs a mini 'stellarmate' network nearby which is great for when you need to be at the scope (PAA, first focus after trying a new setup).
The really nice part is it's agnostic to where it gets it's internet from... so if I'm at home it goes to my house. If I'm away and running on a hotspot/Starlink, I just use the same SSID and it connects to that network. Really cool .