A question about how to use abstract types and typeclasses

UsingShow.scala

package examples
import cats._
import cats.data._
import cats.implicits._
import cats.syntax.show._

class UsingShow1 {
  type Value <: Show[Value]
  
  def showValues(vs: List[Value]): String = 
    ???
    // Doesn't work
    // vs.map(implicitly[Show[Value]].show(_)).mkString
  
}

class UsingShow2[Value: Show] {
  
  def showValues(vs: List[Value]): String = 
    vs.map(implicitly[Show[Value]].show(_)).mkString
  
}