MobileSheets can run as an x86 application. I think going forward I may just completely drop ARM from the list of supported architectures on Windows, as I have several libraries that aren't compiled for ARM64 that I rely on. If you find that you can't run MobileSheets after updating, backup your application data if needed (copy C:\Users\<your username>\AppData\Local\Packages\41730Zubersoft.MobileSheets_ys1c8ct2g6ypr\LocalState somewhere safe), uninstall MobileSheets and try to install it off the Microsoft Store. Hopefully it will pick the x86 version for your device, and then you can copy your library data back to the same installation folder.
Mike
Mike