When I toggle on the install via USB in developer mode:
Turning off Wi-Fi and enabling Mobile Data (thank you Xiaomi for wasting my money to enabling mobile data which the last one I didn't have) on Xiaomi 4A did not work for me. Every time I tried to enable Install App Via USB it displayed me "the device is temporarily restricted". So, I found this solution:
Turn on VPN onto your device with these parameters and try again toggle Install from USB:
China server from https://www.vpngate.net/en/vpn vpn vpn