Upgrading miui12.5 may lead to the problem of slow charging of Millet 10s, because miui12.5 update may change the system Settings, resulting in different battery management strategies, thus affecting the charging speed.
Try clearing your phone's cache, closing unnecessary background apps, or replacing it with an original charger. If the problem still exists, you can try to reset the phone or contact the Xiaomi after-sales service center for processing.
The upgrade will not cause the charge to slow down, you can restart the phone or re-plug the charger socket, you can solve the problem.