Realmec25s issue

With the Realme 25s been a budget phone, it does use a very cheap Realtek processor, and those tend to have a rather poor performance. Which might not be good for gaming. There's probably nothing you can do about that, apart from using a better/faster device, that's it.

As for charging while playing the game. Are you using the original Realme charger or some third-party one?

 

A third party would mean a charger not supplied by the manufacturer of the device.

Like if you bought a charger from somewhere else.

 

Playing games will cause it to charge slow.

Doing anything with it while it charges slows down the charging.