My programm compiles everything and i got no errors, but i actually expected that the tomcat should be on port 8080 permanently. Also there is no Spring in the Output.
On a other project i did everything works fine. Thank u for helping me.

My Parent-Pom:

    <?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <artifactId>spring-boot-starter-parent</artifactId>
        <groupId>org.springframework.boot</groupId>
        <version>2.6.6</version>
        <relativePath/>
    </parent>

    <groupId>org.example</groupId>
    <artifactId>CalculatorWithRest</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>

    <modules>
        <module>app</module>
        <module>infrastructure</module>
        <module>domain-api</module>
        <module>domain-core</module>
        <module>rest-api</module>
    </modules>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.example</groupId>
                <artifactId>app</artifactId>
                <version>${project.version}</version>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <version>2.7.0</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
        </dependency>
    </dependencies>

    <build>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-maven-plugin</artifactId>
                    <configuration>
                        <skip>true</skip>
                    </configuration>
                </plugin>
            </plugins>
        </pluginManagement>
    </build>
    <properties>
        <maven.compiler.source>16</maven.compiler.source>
        <maven.compiler.target>16</maven.compiler.target>
    </properties>
</project>

My Starter.class:

package de.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class appstarter {
    public static void main(String[] args) {
        SpringApplication.run(appstarter.class, args);
    }
}

My Starter-Pom:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>CalculatorWithRest</artifactId>
        <groupId>org.example</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>app</artifactId>

    <properties>
        <maven.compiler.source>16</maven.compiler.source>
        <maven.compiler.target>16</maven.compiler.target>
    </properties>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <skip>false</skip>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

Console Output:

[INFO] --- maven-compiler-plugin:3.8.1:testCompile (default-testCompile) @ rest-api ---
[INFO]
[INFO] CalculatorWithRest ................................. SUCCESS [  1.215 s]
[INFO] app ................................................ SUCCESS [  5.278 s]
[INFO] domain-api ......................................... SUCCESS [  3.251 s]
[INFO] infrastructure ..................................... SUCCESS [  3.075 s]
[INFO] domain-core ........................................ SUCCESS [  2.434 s]
[INFO] rest-api ........................................... SUCCESS [  2.871 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  18.843 s
[INFO] Finished at: 2022-07-26T15:49:58+02:00
[INFO] ------------------------------------------------------------------------

Then nothing happens anymore.
Ty for helping.

>Solution :

I don’t see any dependency on

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

that starts the embedded tomcat. I think you should add this in your app pom.