Solved! I feel a bit stupid - after I posted this it occurred to me to just try rebooting the tablet - and it worked!
Once I got the app working I was a bit disappointed that it doesn't do tablet-friendly landscape mode. Hopefully that will be added to later versions.
Most importantly though, just played my first game, and loved it. The connection with the board and the pieces works perfectly. I'm looking forward to years of online chess with less eyestrain!
And I hope this post may help anyone who forgets to try rebooting like I did! :-)
My Chessnut air arrived today, which was wonderful. The hours of frustration since then have not been so wonderful.
I cannot get the Chessnut app working at all, it won't even open. First my tablet (Samsung Galaxy Tab A7 running Android 12) refused to install it as it said the app was from an "unknown source". A lot of confusing Googling with different advice eventually helped me give the Files app permission to install it.
Now the Chessnut app is installed, but when I click on it, it just takes me to the "All Files Access" section of the tablet's Settings. It seemed a bit outrageous to give Chessnut permission to access all the files on my tablet, but the app did nothing except take me to that part of Settings, so I enabled permission. This had no effect whatsoever. Now, even with permission enabled, when I tap on the Chessnut app it just keeps taking me back to "All Files Access".
Also, when I try to connect the Chessnut Air board to Bluetooth, I get the message "An app is needed to use this device", even though I've installed the app! I click "Pair" and again, nothing happens.
Please don't ask me to use my phone instead. One of the reasons I got the Chessnut Air is so I can have chess.com up on my tablet beside the board and go to Game Review straight after the game - I find a phone just too small for this.
Any help with this would be much appreciated!