Problems assigning separate ringtones to SIM1 and SIM2

[CRFCRE]

I have a Xiaomi Redmi Note 9S and have recently installed a second SIM card for work communications. The dialogue boxes which should appear at the top of the ringtones page to allow the user to allocate ringtones to an individual SIM card are not there. Is this a fault or is this a design issue with MIUI 12?

I note that this appears to be a problem with the Mi10 also.