I'm not sure but clicking on that message android system should offer option to fix this.
Anybody try that?
Don't use my advice.
Seems there is an conflicting situation between Rigol application and Android operating system.
I did it and formatting hang at 20%
I could leave it as is but ...
Next step was factory reset from android menu , also don't do this.
After restart I get a bootloop with only some quick flashing text on screen.
Power cycle few times and started with circle logo and erasing message of android recovery.
And the problems begin
Android see storage partition and all OK
Rigol app report negative size.
adb can't connect anymore getting message on screen remote cmd error but in the end I was able to connect only with Total Commander and their plugin
And worst of all trigger malfunction.
What that means is when turn trigger knob I get a violet line on screen and also colour of trigger on top bar change to violet too and no adjustment available.
Try to calibrate no fix,
Overwrite Rigol folder from backup no fix.
Maybe after few power cycle Rigol app "fix" somehow storage partition as I can see that size is pozitive and no more negative as before,but now android complain again about that problem.
Also try to update firmware but no go, getting only execution failure when select update file and try to update.
Anyway for further investigation I did a full backup by this method
https://www.eevblog.com/forum/testgear/hacking-the-rigol-dho800900-scope/msg5182476/#msg5182476and restored original backup on sdcard, also made with this method
As a note
First time I try from adb console to restore backup, to avoid opening the scope but i killed it, started to write and after some time suddenly (not finished writing) restarted and no more started again so I need to open and write card with external tools.
After that all was fine again.
Taking a quick look at "damaged" backup I can see just in first screen on winhex that are different,looking like some UEFI style partition, didn't check more as lack of time but winhex recognize from start this is an disk image and showing three partitions (but unable to show files) while with original backup can't detect any partition even if I choose this is a disk image.
So android reset change something as is expect to be, but incompatible with Rigol app format.
For those who want to experiment more maybe a launcher or a file browser can be added to Rigol App folder with name help.apk or help_en.apk I don't know if are standalone application one for chinese one for english or parent-child so help is main app and help_en is loaded in case english is selected.
And for missing keyboard maybe installing some version of gboard apk will fix this, if android manage to acces it.
After other problems detected by others now we see problems at level os-application, in the end that looks like an unfinished product or applications made in hurry without basic requirements fixed.