Pop-up cannot be enabled by default. Another way is to keep the pop up from closing when pressed on the map or other markers on the map.
See the below example.
closeButton, closeOnClick disables popup from closing when clicked on other markers and on the map.
leaflet() %>% addTiles() %>% addCircleMarkers(lng=77.6944, lat=12.9811,popup = "My Office",color = "red",popupOptions = popupOptions(closeButton=F, closeOnClick=F))
Hope it helps!