Arduino IDE 1.8.12 crashes on macOS 10.15.5 when clicking scrollbar

Version: Arduino 1.8.12, but also occurs in 1.8.10 and latest hourly build
OS: macOS 10.15.5 (Beta) - Currently available as Developer preview

The IDE starts up okay, and after navigating the various security warnings dialogs from the OS, I can use the ID as usual. However, as soon as I click a scrollbar for one of the text editor tabs, the application crashes with the following error:

```
Application Specific Information:
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCompositeAppearance _callCoreUIWithBlock:options:]: unrecognized selector sent to instance 0x600001a70880'
abort() called
terminating with uncaught exception of type NSException
```

Start by reproducing the scrollbar crash with Arduino IDE 1.8.12 on macOS 10.15.5 and review the reported NSInvalidArgumentException. Done means clicking a text-editor scrollbar no longer terminates the application; the issue does not name a file or test to begin with.

Written by the indexing model from the issue text.