ADDITIONAL SYSTEM INFORMATION :
Ubuntu 20.04.3
Kernel 5.11.0-27
glibc: 2.64.6-1
Thread Library: NPTL 2.31
java 11.0.12
graphics card Amd Radeon RX 6600 XT
Driver: 21.30 open source driver

VM Options:
-Xmx12288m
-Xms6144m
-Djava.util.Arrays.useLegacyMergeSort=true
-Dawt.useSystemAAFontSettings=lcd_hrgb
-Dsun.net.http.allowRestrictedHeaders=true
-Dsun.java2d.uiScale.enabled=false
-Djxbrowser.logging.level=INFO
-Dsun.java2d.opengl=true
-Dsun.awt.disableMixing=true


A DESCRIPTION OF THE PROBLEM :
If both sun.java2d.opengl and sun.java2d.opengl.fbobject are enabled, pop up message box becomes translucent. The issue disappears when sun.java2d.opengl.fbobject is set to false. The issue happens with Amd and Nvdia graphics card.