Am I doing something wrong or substituting elements of environment does not work?

CannotSubstituteMyClock.scala

//> using dep "dev.zio::zio:2.0.15"
//> using scala 2.13

import zio._

import java.time
import java.time.temporal.ChronoUnit
import java.time.{Instant, LocalDateTime, OffsetDateTime}
import java.util.concurrent.TimeUnit

object CannotSubstituteMyClock {

  def main(args: Array[String]): Unit =
    Unsafe.unsafe { implicit unsafe =>
      zio.Runtime.default.mapEnvironment(env => env.add[Clock](MyClock)).unsafe.runToFuture(
        ZIO.clock.map(_.toString).debug("clock") *>
        Clock.currentDateTime.debug("time")
      )
    }
}

object MyClock extends Clock {
  override def currentTime(unit: => TimeUnit)(implicit trace: Trace): UIO[Long] = ???

  override def currentTime(unit: => ChronoUnit)(implicit trace: Trace, d: DummyImplicit): UIO[Long] = ???

  override def currentDateTime(implicit trace: Trace): UIO[OffsetDateTime] = ???

  override def instant(implicit trace: Trace): UIO[Instant] = ???

  override def javaClock(implicit trace: Trace): UIO[time.Clock] = ???

  override def localDateTime(implicit trace: Trace): UIO[LocalDateTime] = ???

  override def nanoTime(implicit trace: Trace): UIO[Long] = ???

  override def scheduler(implicit trace: Trace): UIO[Scheduler] = ???

  override def sleep(duration: => zio.Duration)(implicit trace: Trace): UIO[Unit] = ???

  override def toString: String = "MyClock"
}