Thank you very much again for your kind support !!
Unfortunately neither your modules nor my 'patchwork' are able to restore the 'F_M_Test' App; that is, yes, they reintroduce it, even as a System App, but in any case there is no way to make it work... :-(
So, all in all, also due to some other issues I'm experiencing, I really think I'll reinstall the 'xiaomi.eu_multi_HMNote9ProEU_V12.0.3.0.QJZMIXM_v12-10'...
and to say that my wife (she also has the RN9Pro) had told me SEVERAL times not to update to the first version of Android 11... !!