Is there any alternative to ggtern in R?

Its looks like that ggtern has not been synchronised with new version of ggplot2. Therefore we can not use ggtern.

library(ggtern)
set.seed(1)
plot <- ggtern(data = data.frame(x = runif(100),
                                 y = runif(100),
                                 z = runif(100)),
               aes(x, y, z))
plot + stat_density_tern(geom = 'polygon',
                         n         = 200,
                         aes(fill  = ..level..,
                             alpha = ..level..)) +
  geom_point() +
  theme_rgbw() +
  labs(title = "Example Density/Contour Plot")    +
  scale_fill_gradient(low = "blue",high = "red")  +
  guides(color = "none", fill = "none", alpha = "none")

Error: geom_point requires the following missing aesthetics: x and y

Does anyone have in find other options for ternary diagrams apart from ggtern in R?

Manually, you could plot the points with a function: (I used the formulas at https://en.wikipedia.org/wiki/Ternary_plot)

I'm not familiar with the output of stat_density_tern so I'm not sure what is expected from that part.

library(tidyverse)
tern <- function(df) {
  df %>% mutate(x_pos = 0.5 * (2*y + z) / (x+y+z),
                y_pos = sqrt(3) / 2 * z / (x+y+z)) 
}

tern(plot) %>%
  ggplot(aes(x_pos, y_pos)) +
  geom_point() +
  annotate("path", x = c(0, 0.5, 1, 0), y = c(0,sqrt(3)/2,0,0)) +
  coord_equal()