Run through my GPU guide below and check to see if you have made any errors, if this doesn't work we can try a few other things

The new AMD Adrenalin 2020 Control Center is designed to give support for your hardware and contains Mobile Driver support for this exact model, the Graphics Drivers on the Acer site are only base drivers. If you haven't already downloaded and installed it then click the link below to download it. 
https://www.amd.com/en/support/kb/release-notes/rn-rad-win-20-3-1

Most of the problems I have encountered answering questions similar to yours are that users do not have the GPU set up correctly in the Control Center and are gaming on their Dedicated Vega 8 GPU which gives poor performance and is not designed for gaming. I have your exact model and my gaming experience using the AMD 2020 Control Center is good, Follow these instructions

First make sure you game with your battery charged to 100% BEFORE gaming and KEEP plugged into the main AC power while gaming. Make sure "High Performance when on AC", is selected in your Windows Power Plan and in Nitrosense. If you fail to do this your CPU will run at around 50% of capacity and you will experience poor game performance

Open the New AMD 2020 Control Center and click the GAMING tab then click the 3 dots in the upper right hand corner and select ADD A GAME, navigate to your games .exe file and double click it to add it, or you can select SCAN FOR GAMES and let the Control Center search your harddrive for games to add. After successfully adding the game click on the game and you will be taken to another window and click the LAUNCH GAME tab.
NEVER launch your game through a desktop shortcut or any other way, do it in the manner I have described.

Please remember that online gaming may experience low fps and stutter due to the games servers and bottlenecking and that has nothing to do with your GPU.

PLEASE CLICK YES IF I HAVE ANSWERED YOUR QUESTION, THANKYOU

Zidaaan said:

king5483 said:

update your gpu driver

I already did.its the latest version

Check temperature when there is lag/or fps drop check in nitrosense then tell us