Most likely you have too many programs are on the startup, which and slow down the laptop.
I suggest you to read this article https://tehnichka.pro/startup-macos-how-add-remove...
and the instructions to go to the "login items" to see how many programs at startup. And if you don't want to remove the autorun completely, you can configure a delayed start for the same instructions.
Well and if does not help, then the best option will probably be to reset MacBook to factory settings.