Go in Device Care, click on battery, more battery settings and enable Fast Charging
If it doesn't work, go in Device Care application and clear cache and data and restart your device...
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If you connect the charger that supports fast charging while the fast charging feature is deactivated, the popup window can appear. At that time, please turn on the Fast charging to get the best charging speed from the connected charger. To use the fast charging feature, the fast charging feature must be activated and you must use the approved battery charger that guarantees the charging performance.
You cannot use the fast charging feature or the super-fast charging feature when you charge the battery using a standard battery charger. To use a fast or super-fast charging feature, Fast charging or Superfast charging feature must be activated. To activate this, Settings> Battery and device care> Battery> More battery settings, and then tap the Fast charging or Superfast charging switch to activate it.
Galaxy S21 series supports various charging methods such as AFC(Adaptive Fast Charging), QC 2.0(Quick Charge 2.0), and USB PD(Power Delivery) for wired charging, WPC(Qi), and PMA(Power Matters Alliance) for wireless charging. When using a charger, it is recommended to use an approved wired or wireless charger that guarantees the charging performance. An incompatible battery, charger, and cable can cause serious injuries or damage to your device, and charging may not work properly.
Also, follow the suggestions provided by our members and get back to us with the result.