Spotlight on MacOS can be heavy on the CPU usage. If you want to switch it off you then you will have to run a command in the terminal. Spotlight does provide some very nice functioniality, I don’t use spotlight itself. I use Alfred 3 which uses the same index data. If you disable Spotlight search then Alfred 3 will also stop working.
Command to disable Spotlight
Command to enable Spotlight
Improve Spotlight CPU
You can go through the app settings to improve fix and improve the CPU usage of Spotlight. untick any folders or file types which you never need to search for. Limit the search scope as much as you can for the best performance.