https://stackoverflow.com/questions/69449905/how-to-enable-spring-boot-live-dev-tools-on-intellij-2021-2-to-rebuild-classes-a

2)In IntellijIDEA: go in settings(ctrl +alt+s) -> Build,Execution,Deployment -> compiler, check "Build project automatically"

3) Enable option 'allow auto-make to start even if developed application is currently running' in Settings -> Advanced Settings under compiler 

You can now restart your intelliJ IDE and start your application.