In order to fulfill the basic functions of our service, the user hereby agrees to allow Xiaomi to collect, process and use personal information which shall include but not be limited to written threads, pictures, comments, replies in the Mi Community, and relevant data types listed in Xiaomi's Private Policy. By selecting "Agree", you agree to Xiaomi's Private Policy and Content Policy .
With the latest Pie release V10.3.1.0.PEIMIXM, you cannot use Hotpot along with WIFI. If you want to use this feature, then you have to rollback to the last version ROM i.e. V10.3.1.0.OEIMIXM (after unlocking the device bootloader, so that you don't brick your phone)
Not sure, why Xiaomi has designed (modified the Pie OS) that way; since devices built by other companies like Samsung still has the parallel wifi-hostpot feature available with Android Pie version.