R5 Graphics you have has 384SP (6CU) at 720MHz., although it should be noted in Laptops, power savings behaviour will typically dictate performance.
So unlike the Desktop APU, depending on what is more in demand (Graphics or Processor) this will result in one of the other being able to run at their "Full" Clock.
On top of this as the Battery Lowers (i.e. 90% >> 75% >> 50% >> etc.) so too will the CPU and GPU begin to reduce clocks to save Battery Life.
League of Legends is typically a CPU intensive game, and that's the component that will use the most Power.
(the R5 used is GCN 1.1 which is quite power efficient)
Plugging in the Laptop to the Wall and disabling "Power Saving" mode in Windows (which in Windows 10 is a little too focused on Battery Life., which running more damn apps that drain it quicker) means your performance will generally drop over time.
This is perhaps going to be worse ATM given Spectre and Meltdown Windows Patches have added some runtime performance that is normally negligible on Desktops but might trigger a more aggressive Power Saving on Laptops.
First of all, thanks for all the information given
My laptop is usually plugged to the charger 24/7, so I don't know what I could change tbh.
Disable power saving mode.
sorry for my late response! I did so but unfortionately its not working.
What else could I do?