Исходный код

penguins |> 
  na.omit() |> 
  ggplot(aes(x = bill_length_mm,
             y = bill_depth_mm,
             fill = species,
             size = body_mass_g))

Видоизмененный код

penguins |> 
  na.omit() |> 
  ggplot(aes(x = bill_length_mm,
             y = bill_depth_mm,
             fill = species,
             size = body_mass_g)) + 
  geom_point(pch = 21,
             color = "white", 
             alpha = 0.7)