Are you running any anti-virus software, cleaning/optimizer apps, or third party security software? If so, then uninstall them by following the developer's instructions since these types of apps are not needed on a Mac and usually causes more problems than they solve because they interfere with the normal operation of macOS.
Your system may also still be configuring itself after the migration or restoration from a backup. Spotlight will definitely be indexing the system and if you have enabled any cloud file syncing services, then those will also be doing a lot of work.
And make sure all your third party apps are completely up to date.