You may download the latest BIOS updates here for your specific motherboard: https://www.asus.com/us/Motherboards/PRIME-B350-PLUS/HelpDesk_BIOS/ Just make sure that your motherboard is the correct model.
Warning: Just ensure that BIOS flash does NOT get interrupted by anything, e.g blackout, because if anything interrupts the BIOS flash, you can brick your motherboard (Some motherboards have dual BIOS but this one may not).
1. When you have downloaded the latest BIOS, get a USB stick (make sure there's nothing inside it and single partition) and format it to FAT32. Then put the file inside the zip file (ends with .CAP) into the USB.
2. Now restart your PC to UEFI, go to Advanced Mode, go to the 'Tools' tab, and go to EZ Flash 3 Update.
3. Choose USB as your method of updating the BIOS.
4. Look for the USB drive that contains the .CAP file, then select it. It will ask you to confirm the BIOS update. This is your last chance to check if the BIOS update is correct and specific for your motherboard. The link I have given you was for the PRIME B350-PLUS motherboard.
***From this point, you do NOT want anything interrupting the BIOS update/flash***
5. It will now proceed with the update. If it was successful, it will let you know, and that the system will restart.
6. Once it has restarted, it will return to the UEFI and you will get a prompt that you gotta select the same BIOS file to continue updating.
7. Repeat steps 3 and 4. After selecting the same BIOS once again, it will ask you to confirm if you really want to update the BIOS. If you want to continue, say yes.
8. It will process again, and will need to restart after it has successfully updated.
9. Once it has restarted, you are done. It may take you to the "American Megatrends" screen where it asks you to recover BIOS setting. Just proceed and change some settings to your likings (make sure you know what you are tweaking. Once you are finished, you may save and exit, and proceed to Windows.
Play the games that you usually play and check if you still get the same horrible performance. I hope this solution helped.