The first problem was,
that I ecexuted the Jar file in a wrong way.
I did
java metaDataDB-0.5-msSQL.jar -login:login.txt
The right way to do it:
java -jar metaDataDB-0.5-msSQL.jar -login:login.txt
After that, I realized that I didn't include the dependency needed into my Jar.
I've learned what a Fat Jar File is.
So I needed to add this to my gradle jar task:
 from{
        configurations.runtimeClasspath.collect {it.isDirectory() ? it: zipTree(it)}
    }
For referencere my whole build.gradle file:
plugins {
    id 'java'
}
jar{
    manifest {
        attributes ('Main-Class': 'metaDataDB.Main')
    }
    from{
        configurations.runtimeClasspath.collect {it.isDirectory() ? it: zipTree(it)}
    }
}
repositories {
    mavenCentral()
}
group 'com.dvb'
//version '1.0-SNAPSHOT'
version '0.5-msSQL'
sourceCompatibility = 17
dependencies {
    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.8.2'
    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.8.2'
    // https://mvnrepository.com/artifact/org.postgresql/postgresql
   // implementation group: 'org.postgresql', name: 'postgresql', version: '42.3.1'
    implementation 'com.microsoft.sqlserver:mssql-jdbc:10.1.0.jre17-preview'
    // / https://mvnrepository.com/artifact/com.microsoft.sqlserver/mssql-jdbc
    // https://mvnrepository.com/artifact/com.microsoft.sqlserver/mssql-jdbc
    //implementation 'com.microsoft.sqlserver:mssql-jdbc:9.2.1.jre15'
}
test {
    useJUnitPlatform()
}
That worked for the postgressql Driver.
For the Microsoft SQL Drivers a new Problem came up.
java -jar metaDataDB-0.5-msSQL.jar -login:ms.txt
Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.SecurityException: Invalid signature file digest for Manifest main attributes
        at java.base/sun.security.util.SignatureFileVerifier.processImpl(SignatureFileVerifier.java:340)
        at java.base/sun.security.util.SignatureFileVerifier.process(SignatureFileVerifier.java:282)
        at java.base/java.util.jar.JarVerifier.processEntry(JarVerifier.java:277)
        at java.base/java.util.jar.JarVerifier.update(JarVerifier.java:234)
        at java.base/java.util.jar.JarFile.initializeVerifier(JarFile.java:762)
        at java.base/java.util.jar.JarFile.ensureInitialization(JarFile.java:1033)
        at java.base/java.util.jar.JavaUtilJarAccessImpl.ensureInitialization(JavaUtilJarAccessImpl.java:72)
        at java.base/jdk.internal.loader.URLClassPath$JarLoader$2.getManifest(URLClassPath.java:883)
        at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:848)
        at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:760)
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:681)
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:639)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
        at java.base/java.lang.Class.forName0(Native Method)
        at java.base/java.lang.Class.forName(Class.java:467)
        at java.base/sun.launcher.LauncherHelper.loadMainClass(LauncherHelper.java:780)
        at java.base/sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:675)
here a link to the exception:
https://learn.microsoft.com/de-de/dotnet/api/system.security.securityexception?view=net-6.0
I tried it to run in adminstrator mode, but that failed too...
But I guess this is a new question, and hasn't to do anything with gradle.
I guess the answer to "Building a Jar using gradle - Jar hasn't sql dependency" is answered.
I will create a new Question for the microsoft sql driver and link it here.
(I hope I did everything right)