I would not recommend installing a BIOS update. On Asus laptops, this can disable CPU voltage control. A BIOS update might end up making a laptop run worse, not better, with no easy way to go back to the previous version. Asus likes to hide older laptop BIOS versions from their website. He used to be able to play games smoothly so something not related to the BIOS has recently changed.
@imacrypleasehelp
Download ThrottleStop.
ThrottleStop is a small application designed to monitor for and correct the three main types of CPU throttling that are being used on many lapto
www.techpowerup.com
Post some screenshots of ThrottleStop including the FIVR, TPL and Limit Reasons windows. You can use imgur to host your screenshots. Turn on the Log File option on the main screen and go play a game for 10 or 15 minutes. Before you do this, open the Options window and check the Nvidia GPU box on the right side so your GPU temperatures and GPU MHz data will be included in the log file.
When done testing, exit ThrottleStop so it can finalize your log file. It will be in your ThrottleStop / Logs directory. Copy and paste the log file data to
www.pastebin.com and then post a link here so I can have a look. If your computer is suddenly performing terribly, something should show up in the log file to explain why.