Opening relation editor disables all input and necessitates force quit since updating to MacOS 11 (Big Sur)

[rideearthtom]

What steps will reproduce the problem?

1. Freshly install latest JOSM.app
2. Open any dataset
3. Open relation editor

What is the expected result?

Relation editor modal opens and works normally

What happens instead?

Relation editor opens as a tab and disables all input (trackpad/keyboard) for the entire app, including menu bar, necessitating force quit.

Please provide any additional information below. Attach a screenshot if possible.

I use JOSM professionally and have been unable to work for several weeks since updating to the latest version of MacOS. There appears to be some kind of windowing issue with the combination of OS and software.

I have taken every possible action I can think of to remedy this, including uninstalling both JOSM and Java, reinstalling the latest version using Homebrew, the Mac package and the Java webstart versions, deleting all of the files in ~/Library, ~/Library/Preferences and ~/Library/Caches, including all .plist files and other preference files, and the problem persists.

My last resort is to format my MacBook and reinstall an earlier version of MacOS in the hope that this will solve things, but I'd prefer to see if there's a known fix before taking such a drastic step.

Revision:17580
Build-Date:2021-03-18 15:54:45

Identification: JOSM/1.5 (17580 en_GB) Mac OS X 10.16
OS Build number: macOS 11.2.3 (20D91)
Memory Usage: 328 MB / 8192 MB (104 MB allocated, but free)
Java version: 16+36, Azul Systems, Inc., OpenJDK 64-Bit Server VM
Look and Feel: com.apple.laf.AquaLookAndFeel
Screen: Display 69731840 1280×800 (scaling 2.00×2.00)
Maximum Screen Size: 1280×800
Best cursor sizes: 16×16→16×16, 32×32→32×32
VM arguments: [-Djpackage.app-version=17580, --add-exports=java.desktop/com.apple.eawt=ALL-UNNAMED, --add-exports=java.desktop/com.sun.imageio.plugins.jpeg=ALL-UNNAMED, --add-exports=java.desktop/com.sun.imageio.spi=ALL-UNNAMED, --add-opens=java.base/java.lang=ALL-UNNAMED, --add-opens=java.base/java.nio=ALL-UNNAMED, --add-opens=java.base/jdk.internal.loader=ALL-UNNAMED, --add-opens=java.base/jdk.internal.ref=ALL-UNNAMED, --add-opens=java.desktop/javax.imageio.spi=ALL-UNNAMED, --add-opens=java.desktop/javax.swing.text.html=ALL-UNNAMED, --add-opens=java.prefs/java.util.prefs=ALL-UNNAMED, -Djpackage.app-path=/Applications/JOSM.app/Contents/MacOS/JOSM]