On a Samsung Galaxy A21s, fundamental operations like turning the phone on or off are no longer feasible once the power button stops working. So, while a service repair is still pending, we have planned out alternative ways to use the phone.
The whole manual is provided below:
Samsung hardware problems that prevent the power button from functioning can only be remedied by sending the Samsung in for service. Even if you are unable to fix your Samsung or it has passed its warranty, the situation is not yet finished. The above are some instructions for utilizing your Galaxy A21s without a power button.
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