Huawei
Enable or Disable Dual 4G auf Huawei
On Huawei phones with two SIM cards, only one card gets full 4G speed by default in some setups, while the second card falls back to 3G or 2G. This is controlled by a single toggle in the mobile network settings, not by the SIM cards themselves or your carrier.
The setting is called Dual SIM 4G. When it is off, the phone reserves the fast network for one SIM and pushes the other to a slower connection whenever both are active. Turning it on lets both SIM cards connect via 4G at the same time, which is useful if you use one number for calls and the other for mobile data.
To change it, open Settings ➔ Mobile network ➔ SIM management and activate or deactivate Dual SIM 4G.
Keep in mind that running both SIM cards on 4G at once increases power draw, since the modem keeps two high-speed connections alive instead of one. If your device runs warm or the battery drains faster after enabling this, switching it back off restores the single-4G behavior without disabling either SIM.