st_bbox_to_poly

st_bbox_to_poly <- function (bbox) {
  x1 <- bbox[1]
  y1 <- bbox[2]
  x2 <- bbox[3]
  y2 <- bbox[4]
  
  sf::st_polygon(list(matrix(c(
    x1, y1,
    x1, y2,
    x2, y2,
    x2, y1,
    x1, y1
  ), ncol = 2, byrow = TRUE)))
}

## give it your bounding box
st_bbox_to_poly(shape) %>% 
  sf::st_sfc(crs = 4326) %>% 
  mapview::mapview() 

poly <- st_bbox_to_poly(shape) %>% 
  sf::st_sfc(crs = 4326) %>% st_as_sf()

geojsonsf::sf_geojson(poly)