question
The project has added spring-boot-starter-web dependency, @SpringBootApplication is still popular
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
solve
Typically, when you introduce or remove dependencies, change the project structure, or make other important configuration changes in a Maven project, you may need to execute the mvn idea:clean command to clean and regenerate the IntelliJ IDEA project files and configuration.
mvn idea:clean