Can you also help me with the screenshot of activity monitor with memory tab please? And, can you tell me if you have ran a diagnostic test on your computer recently? Do you use any applications now which are not compatible with Catalina and work only on BigSur ? What exactly did Apple tell you as a solution when you contacted the support people? Have you ever take this laptop to the Apple Authorised Service Centre to get it checked up? Have you ran an Antivirus scan on your laptop recently? Did you reset the PVRAM and NVRAM of your Mac too when you were troubleshooting the issue?
I also recommend you not to run Asphalt 9 kind of games as they use huge amount of CPU and memory and with i3 CPU it is not suitable for gaming.
If you do not have any applications not compatible with Catalina and if you want to go back to macOS Catalina I can help you go back ( if you would like to downgrade and use Catalina until BigSur becomes bit stable for you.).
Anyway, please share the requested info for me to proceed to help you in an even better way.
Thanks!