Trying to get the types in dotty to line up.

PointedGraph.scala

package org.w3.banana

import org.w3.banana._

trait RDFOps[Rdf <: RDF & Singleton](using val Rdf: RDF) {
   def emptyGraph: Rdf.Graph
}


trait PointedGraph[Rdf <: RDF & Singleton](using val ops: RDFOps[Rdf]) {
  def pointer: ops.Rdf.Node
  def graph: ops.Rdf.Graph
}

object PointedGraph {
  def apply[Rdf <: RDF & Singleton](using ops: RDFOps[Rdf])(
    node: ops.Rdf.Node,
    inGraph: ops.Rdf.Graph
  ): PointedGraph[ops.Rdf.type] =
    new PointedGraph[ops.Rdf.type](){
      val pointer = node
      val graph = inGraph
    }

  def apply[Rdf <: RDF & Singleton](using ops: RDFOps[Rdf])(node: ops.Rdf.Node): PointedGraph[ops.Rdf.type] =
    this.apply[ops.Rdf.type]()(node, ops.emptyGraph)

  def unapply[Rdf <: RDF & Singleton](using ops: RDFOps[Rdf])(
    pg: PointedGraph[ops.Rdf.type]
  ): (pg.ops.Rdf.Node, pg.ops.Rdf.Graph) = (pg.pointer, pg.graph)

}

Ok this compiles:

package org.w3.banana

import org.w3.banana._

trait RDFOps[T <: RDF & Singleton](using val rdf: T) {
   def emptyGraph: rdf.Graph
}


trait PointedGraph[T <: RDF & Singleton](using val rdf: T) {
  def pointer: rdf.Node
  def graph: rdf.Graph
}

object PointedGraph {
  def apply[T <: RDF & Singleton](using rdf:T)(
    node: rdf.Node,
    inGraph: rdf.Graph
  ): PointedGraph[rdf.type] =
    new PointedGraph[rdf.type](){
      val pointer = node
      val graph = inGraph
    }

  def apply[T <: RDF & Singleton](using rdf: T) (
    node: rdf.Node
  )(using ops: RDFOps[rdf.type]): PointedGraph[rdf.type] =
    new PointedGraph[rdf.type]() {
      val pointer = node
      val graph   = ops.emptyGraph
    }

  def unapply[T <: RDF & Singleton](using rdf: T)(
    pg: PointedGraph[rdf.type]
  )(using ops: RDFOps[T]): (rdf.Node, rdf.Graph) = (pg.pointer, pg.graph)

}