creating a nested tibble

Question

I would like to create a tibble that contains a nested tibble, but also a column outside the nested tibble that refers to a column header within the nested tibble. This is what I mean

library(tidyverse)
tib <- tibble(dat = list(tibble(xvar = 1, freq = 2, rate = 3.2)),
              yvar = c(freq)
             )

However I get the error "Error in eval_tidy(xs[[j]], mask) : object 'freq' not found"

I want to use the cell contents of tib$yvar as the input into a function that contains a ggplot function eg.

plot_datapoint <- function(dat = tib){
     dat_tib <- dat %>% unnest(cols = c(dat))

ggplot(dat_tib, aes(x=xvar, y = yvar)+
geom_point()

I believe the solution has something to do with quosures, but don't know how to implement it.