Is there a way to run a single test from the command line if a test framework is used?

not a single test, but you can run a single test file by using the gradle --test a.b.Class

But shouldn't it, at least from a Gradle perspective, also be possible to run a single test case? At least https://docs.gradle.org/current/userguide/java_testing.html#simple_name_pattern says "Gradle has treated a pattern starting with an uppercase letter as a simple class name, or a class name + method name", so a method name should be possible.

Gradle assumes individual test cases are methods, but in Kotest it’s not the case. Afaiu Gradle’s internals are pretty opinionated about tests and there’s a lot of features even from regular JUnit5 that aren’t very well supported

you can filter top level tests: https://github.com/kotest/kotest/issues/329