The two Will Robinsons switch places
Bill and Max: Lost and Found in Space is a special feature included on the first season Blu-ray and DVD releases of the 2018 Lost in Space series. It features Maxwell Jenkins and Bill Mumy as themselves and their characters of both the original and new Will Robinson, and compares the similarities and differences between the original Lost in Space and the new Lost in Space.
The special ends with a short crossover between the two realities, as both Will Robinsons switch places on each other's Jupiter 2, and meet each other's version of the Robot. This special is a sequel to the original Lost in Space Forever special's ending sequence, featuring the return of the amulet as the Probable Reality Disruptor. Dick Tufeld's original Robot voice is also used in the special.
While this was the first crossover released between the original and new series, chronologically the When Worlds Collide two-part crossover story in the Lost in Space Ultimate Collection was the first meeting between the two realities.