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The same issue exists for platforms. I created an issue for this and it was closed, stating that this was never the intention for version catalogs to solve this.

you could create a project containing

plugin {
    id("java-test-fixtures")
}
dependencies {
    testFixturesApi(libs.junit.jupiter.api)
    testFixturesRuntimeOnly(libs.junit.jupiter.engine)
}

or something along those lines, and depend on that?

What @ephemient wrote is also how I solved the issue:

dependencies {
  testImplementation(libs.test.implementation)
  testRuntimeOnly(libs.test.runtime)
}

That said, you actually don't have to include engine in the runtime dependencies for JUnit to work correctly. Just import the BOM (aka. Platform) and tell Gradle to use JUnit 5, should be enough. Maybe you need the API, don't remember.

For things like this (common testing dependencies) - I bundle it all up in to a convention plugin. That plugin also does things like test task configuration, and in turn applies other conventions for things like checkstyle and spotbugs.