Cannot resolve plugin org.springframework.boot:spring-boot-maven-plugin:＜unknown＞

Solution: add version number version to spring-boot-maven-plugin

<build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>2.6.0</version>
            </plugin>
        </plugins>
    </build>