The test fails with JDK20 on all platforms with below error:
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LocalDateTimeStringConverterTest > [0] > test.javafx.util.converter.LocalDateTimeStringConverterTest.testChronologyConsistency[0] FAILED
    org.junit.ComparisonFailure: expected:<..., 60 Shōwa, 12:34:56[ ]PM> but was:<..., 60 Shōwa, 12:34:56[ ]PM>
        at org.junit.Assert.assertEquals(Assert.java:117)
        at org.junit.Assert.assertEquals(Assert.java:146)
        at test.javafx.util.converter.LocalDateTimeStringConverterTest.testChronologyConsistency(LocalDateTimeStringConverterTest.java:160)

LocalDateTimeStringConverterTest > [1] > test.javafx.util.converter.LocalDateTimeStringConverterTest.testChronologyConsistency[1] FAILED
    org.junit.ComparisonFailure: expected:<..., 60 Shōwa, 12:34:56[ ]PM> but was:<..., 60 Shōwa, 12:34:56[ ]PM>
        at org.junit.Assert.assertEquals(Assert.java:117)
        at org.junit.Assert.assertEquals(Assert.java:146)
        at test.javafx.util.converter.LocalDateTimeStringConverterTest.testChronologyConsistency(LocalDateTimeStringConverterTest.java:160)

LocalDateTimeStringConverterTest > [2] > test.javafx.util.converter.LocalDateTimeStringConverterTest.testChronologyConsistency[2] FAILED
    org.junit.ComparisonFailure: expected:<..., 60 Shōwa, 12:34:56[ ]PM> but was:<..., 60 Shōwa, 12:34:56[ ]PM>
        at org.junit.Assert.assertEquals(Assert.java:117)
        at org.junit.Assert.assertEquals(Assert.java:146)
        at test.javafx.util.converter.LocalDateTimeStringConverterTest.testChronologyConsistency(LocalDateTimeStringConverterTest.java:160)
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It will be a must fix before updating boot jdk to 20 OR
before official release of OpenJFX20.(which would be expected to be compatible with JDK20)

At first look it seems like a test bug: There may be a API change in JDK20 to which jfx should adapt to.