This is an extension of Plugin tests are failing on Apple Silicon; see also idea-netcdf-plugin/issues/1
I do not believe this is an issue of trying to run a UI test with com.intellij.testFramework.fixtures.BasePlatformTestCase. All tests work as-is on AMD64 (Intel) platforms, and there are newly failing tests that do not use BastPlatformTestCase.
I have discovered that the tests in question do not fail when using JUnit as the test runner, i.e. a JUnit run configuration in IntelliJ. The tests only fail when using gradle :test on Apple Silicon. Behavior is the same from the command line or an IntelliJ Gradle run configuration.
The project's dev-junit5 branch is configured to use JUnit as a test runner. Running ./gradlew test will show the failing tests, while all tests pass when using a JUnit run configuration in IJ.