The transitive jars lost in .war file when it's in 'provideRuntime' configuration!

The very first line you quoted from the link spends the rest of the paragraph answering your question. In that example, spring-core is commons-httpclient and spring-jcl is commons-codec.

Let’s say you add commons-httpclient:commons-httpclient:3.0 to any of the provided configurations. This dependency has a dependency on commons-codec . Because this is a “provided” configuration, this means that neither of these dependencies will be added to your WAR, even if the commons-codec library is an explicit dependency of your compile configuration. If you don’t want this transitive behavior, simply declare your provided dependencies like commons-httpclient:commons-httpclient:3.0@jar.

In other words, your dependency declaration would look like this:

dependencies { 
    implementation 'org.springframework:spring-jcl:5.1.6.RELEASE'
    providedRuntime 'org.springframework:spring-core:5.1.6.RELEASE@jar'
}