Dick van dyke in new mary poppins
I think you may be mistaken! Dick Van Dyke played the role of Bert, the chimney sweep, in the original 1964 Disney movie "Mary Poppins" alongside Julie Andrews. He did not appear in the 2018 sequel "Mary Poppins Returns".
In the 2018 film, the role of Jack, the lamplighter and friend of Mary Poppins, was played by actor Lin-Manuel Miranda. The movie starred Emily Blunt as Mary Poppins and Ben Whishaw as Michael Banks, the grown-up son of the original Banks children.
Dick Van Dyke did make a special appearance in "Mary Poppins Returns", however. He reprised his role as Bert in a brief cameo, appearing in a scene where Mary Poppins and the children are walking through the streets of London. It was a lovely nod to the original film and a treat for fans of the classic movie!