Same problem here. Really slow after upgraded to Big Sur 11, 11.0.1. Finally fallback to Catalina, Apple please fix this problem.
MacBook Pro (Retina, 13-inch, Mid 2014)
Processor: 2.8 GHz Dual-Core Intel Core i5
Memory: 16 GB 1600 Mhz DDR3
Graphics: Intel Iris 1536MB