VoLTE, NoE. Where has VoLTE gone from the MIUI ruins?

A few days or weeks ago, we were still enjoying the advantages and disadvantages of VoLTE. Faster call set-up and better voice quality for the customer, better capacity utilisation, better quality targets for the operator - these are the benefits of Voice over LTE technology, or VoLTE. The service uses the 4G network, which is known to be not the most sophisticated in our country with Xiaomi phones, as quite a lot of devices lack the B20, the 800 mHz frequency. But it is not only a problem in our country, but in many officially supported countries and therefore it was removed from the settings, although most devices already have it.

Why is the Volte feature disabled on my device? 
1. The modem parameter is incomplete and some carriers are not supported
2. Obtaining VoLTE certification is time-consuming, so vendors will ask for it to be disabled.
3. Need to improve the service provider's network

Countries and regions that support VoLTE:
Mi MIX 2: India, Malaysia, Hong Kong, Taiwan, Cambodia, America, South Korea;
Wed 6: India, Malaysia, Hong Kong, Taiwan, Cambodia, South Korea;
Mi Note 2: India, Malaysia, Hong Kong, Cambodia, South Korea;
Mi A1, Mi 5s, Mi 5s Plus, Mi MIX: India, Malaysia, Hong Kong, Cambodia, South Korea;
Other tools: India, Malaysia

VoLTE has been blocked in other countries. To enable VoLTE service, dial *#*#86583#*#* code. But all risks are borne by the user and we cannot guarantee that the VoLTE feature will work properly once enabled. This solution is temporary. VoLTE will be enabled in the future based on related test results.

Note that this is not a mistake, our country and many others are not listed, so the VoLTE switch is disabled in the ruins.