Hard to say without further info.
Do you notice it being slow for all files, or just specific ones? All languages, or just for certain ones?
What’s the state of your system according to Activity Monitor? (RAM, storage, CPU, etc.)
I have experienced occasional lag on complicated projects, but those usually are related to LSP functionalities (possible same as Very bad performance when using a Language Server - #8 by logan). Otherwise Nova has been mostly quite fast (with many extensions) on my 2017 MacBook Pro.