Version: 2.1.1_0159 is temporarily not supported (!) about z03mmc

[devbis]

It may require additional work from https://github.com/pvvx/ATC_MiThermometer/ project as the current installation heavily relies on the work done by pvvx. You may track pvvx/ATC_MiThermometer#378 for updates.
Additionally, you can solder wires to flash firmware using UART, current fw version won't affect this method.

[VonalOrdu]

To go back to the old version (Original_OTA_Xiaomi_LYWSD03MMC_v1.0.0_0130.bin );
To do this, you must remove your temperature sensor and connect it with the cables by following the steps below.
This is how I solved my problem.
I'm sorry for my bad english.

1. https://github.com/pvvx/ATC_MiThermometer/blob/master/Original_OTA_Xiaomi_LYWSD03MMC_v1.0.0_0130.bin download
2. https://pvvx.github.io/ATC_MiThermometer/USBCOMFlashTx.html
3. 
4. 
5. File select Original_OTA_Xiaomi_LYWSD03MMC_v1.0.0_0130.bin
6. Write to flash

[devbis]

Please, track atc1441/ATC_MiThermometer#298 for updates

[spencermccarthy]

Is it possible to use the Xiaomi BLE integration on this new firmware? I guess not is a BindKey cannot be set.

[devbis]

This firmare is to use the sensor with Zigbee network. For bluetooth support you'd better ask in BLE atc1441/pvvx repos