Unicode Replacement Character (0xFFFD) is displayed in different ways

Reproducers attached.

Unicode Replacement Character (0xFFFD) is displayed in different ways depending on Qt version or/and language used together.

  Qt v5.6.3
     Replacement Character is NOT displayed with either of Thai/Japanese/English.

  Qt v5.7.1
     With Thai: Displayed
     With Japanese/English : NOT displyed

  Qt v5.15.10
     With Thai: Displayed.
     With Japanese/English : Another character is displayed.

  Qt v6.6.1
     Displayed with either of Thai/Japanese/English.

Please see attached screenshots.