[Zubersoft]

I just checked on my Boox Max 2 Pro and the X shows up fine. I'm guessing you have the BOOX optimizations enabled for MobileSheetsPro. As mentioned in other threads, you should disable those if they are currently enabled. To do this, long press MobileSheetsPro on the home page, click "Optimize App", then go to the last tab and there should be a switch to turn all the optimizations off. Alternatively, you can just switch off some of the settings. This should hopefully fix the issue with the X not showing up properly on your device.  If that's not the problem, I can't imagine what else would be causing it not to show up on your device, but I'll have to do some investigation in that case, as then it may be related to the OS version.

Mike