I have read check documentation: https://checkstyle.sourceforge.io/checks/blocks/leftcurly.html
I have downloaded the latest checkstyle from: https://checkstyle.org/cmdline.html#Download_and_Run
I have executed the cli and showed it below, as cli describes the problem better than 1,000 words

Detected at: #14901 (comment)

As per the newly added Exception case in the section 4.1.2 Nonempty blocks: K & R style:

Exception: In places where these rules allow a single statement ending with a semicolon (;), a block of statements can appear, and the opening brace of this block is preceded by a line break. Blocks like these are typically introduced to limit the scope of local variables, for example inside switch statements.

If a block of code appears, then the opening brace ( { ) of that block should be preceded by a line break, for example:

case 42:
  {
    int x = foo();
    frob(x);
  }

Here a block of code appeared and its { is preceded by a line break but Checkstyle does not follow this updated rule, as of now we don't enforce a line break before the { for such code blocks, for example:

/** Testing. */
public class TestingLeftCurly {
  static void testing() {
    int xyz = 10;

    switch (xyz) {
      case 42:
        { // false positive warning
          xyz++;
          foo(xyz);
        }
        break;

      case 10: { // false negative, should give warning here
        xyz++;
        foo(xyz);
      }
      break;

      default:
        break;
    }
  }

  static void foo(int xyz) {
    // do nothing.
  }
}

Output:

$ java -jar .\checkstyle-10.17.0-all.jar -c .\google_checks.xml .\TestingLeftCurly.java
Starting audit...
[WARN] C:\checkstyle testing\TestingGoogleStyle\.\TestingLeftCurly.java:8:9: '{' at column 9 should be on the previous line. [LeftCurly]
Audit done.

As you can see, there's no violation for case 10: { while there should be one. And there is a false positive violation for case 42: \n{ while it is the correctly formatted code.

Describe what you expect in detail.

We should update LeftCurly module in google config to enforce new line before { of such coding blocks and also ensure to give violation if they are misplaces