I ran the following reproducible lines of code and got this:
library(sf)
library(leaflet)
library(osmdata)
roundhay_park_all = opq("leeds") %>%
add_osm_feature(opq = ., key = "name", value = "Roundhay Park") %>%
osmdata_sf()
roundhay_park_multipoly = roundhay_park_all$osm_multipolygons
roundhay_park_poly = roundhay_park_multipoly %>%
st_cast("POLYGON")
leaflet() %>%
addTiles() %>%
addPolygons(data = roundhay_park_poly)

I expected something like this (the shape of Roundhay Park):
plot(roundhay_park_poly$geometry)
