I've dug into this a LOT, and I haven't even seen anything that claims that what I was doing should have ever worked. I was basically using my standard multiplatform tests under Android. These tests launch using runComposeUiTest. When I do that, its runComposeUiTest itself that fails. My composable is never called. And dumping the process name before calling that function shows that IDEA or gradle launched my tests under ${applicationId}, NOT ${applicationId}.test. So runComposeUiTest is launching an intent into ${applicationId}.test (but it is running as ${applicationId}), so fail.
Many sites/AIs I use actually say that runComposeUiTest does not work at all for android. So maybe it was just a bug that it ever worked?
It sucks to not be able to run my GUI unit tests any more. However, if I create an androidInstrumentedTest directory and use the " @get:Rule val composeRule = CreateAndroidComposeRule
..." technique, then I can run an activity under Android. This at least will allow me to create and run a system-level test for Android.