I got it! just replace mm$learners[[1]] with mm$learners[[1]]$model

unified <- unify(mm$learners[[1]]$model, data)
treeshap1 <- treeshap(unified,  data[700:800, ], verbose = 0)
treeshap1$shaps[1:3, 1:6]
plot_contribution(treeshap1, obs = 1, min_max = c(0, 16000000))