This one may be close to the result you need:

ggplot(df_long, aes(x = Variable, y = ID, color = Z_score, size = abs(Z_score))) +
  geom_point() +
  scale_y_discrete(position = "right")+
  facet_grid(rows = vars(Group), scales = "free_y", space = "free_y", switch = 'y') +
  scale_color_gradient2(low = "blue", mid = "white", high = "red", midpoint = 0) +
  theme_minimal() +
  theme(
    axis.text.x = element_text(angle = 45, hjust = 1),
    strip.text.y.left  = element_text(angle = 0)
  ) +
  labs(x = "Variables", y = "Cell Line", color = "Z-Score", size = "Magnitude")