Xiaomi Mi Router 4A Gigabit Edition (R4AG/R4A Gigabit) -- fully supported and flashable with OpenWRTInvasion

well, if you have R4AC global version story is different . try this method :

1-download MIWIFIRepairTool from xiaomi:
2-download chinese firmware 2.18.28:
3-set static ip to your computer
2020-05-19 01_11_45-Internet Protocol Version 4 (TCP_IPv4) Properties
4-Run MIWIFIRepairTool.x86.exe

2020-05-19 01_05_12-СÃ×·ÓÉÆ÷ÐÞ¸´¹¤¾ß

2020-05-19 01_06_56-Settings

2020-05-19 01_07_45-Settings
hold down the Reset button and power on the router then release it after 8 sec and wait for the router to flash the firmware.

After that you can update to 2.18.58 via web interface.