Big Sur is not working properly in my MacBook Air (Retina, 13-inch, 2019)

Big Sur is not working properly in my MacBook Air (Retina, 13-inch, 2019).

Processor: 1.6 GHz Dual-Core Intel Core i5

Memory: 16 GB

It is always gets hanged if you open multiple application at single time and was working fine with previous version. Can you please let me know how to revert back to previous version.