lons = seq(-180, 180, by = 30)
lats = seq(-90, 90, by = 30)

grat = st_graticule(lon = lons, lat = lats)

box = st_bbox(c(xmin = -180, xmax = 180, 
                ymax = 90,   ymin = -90), 
              crs = st_crs(4326)) |> 
  st_as_sfc() |> 
  smoothr::densify(max_distance = 1) 

degree_labels = function(grat, vjust, hjust, size, lon = T, lat = T) {
  pts = grat |>  
    st_cast('POINT') |> 
    group_by(degree, type, degree_label) |> 
    filter(row_number() == 1)
  
  list(
    if (lon) geom_sf_text(data = filter(pts, type == 'E'), vjust = vjust, size = size,
                          mapping = aes(label = degree_label), parse = TRUE),
    if (lat) geom_sf_text(data = filter(pts, type == 'N'), hjust = hjust, size = size,
                          mapping = aes(label = degree_label), parse = TRUE)
  )  
}