Add an opacity slider to a leaflet map generated in r

I would like to add an opacity slider to a leaflet map generated in r. It should change the opacity of the uppermost visible or all visible layers (either of the two, I don’t mind).
I found helpful advice in this thread:
Add opacity slider in R leaflet

This blog:
https://bookdown.org/nicohahn/making_maps_with_r5/docs/leaflet.html

and tried the following two packages, but none of the two seems to work:

leaflet.multiopacity

leaflet.opacity

So I figured out, this should be possible with htmltools. However, I struggle with the following

1. Dragging the slider moves the map too (while changing the opacity of the labels), as pointed out in Laurens comment here: Add opacity slider in R leaflet

2. I would like to change the opacity of the selected overlay layers. However I neither manage to get those values nor to change their opacity value.

Not helpful in this cause is, that I have almost no command of Javascript. Here is an example on how far I got. Would appreciate anyone pointing me into the right direction. I don’t even know how the access variables filled by htmltools javascript commands.

library(leaflet)
library(mapview) #to get the franconia dataset
library(htmltools)

colors <- colorFactor(palette = c("Red", "Green", "Blue"),
                      levels = c("Oberfranken","Mittelfranken", "Unterfranken"))


franconia %>% leaflet() %>% 
  addProviderTiles("CartoDB.Positron", group = "CartoDB.Positron") %>% 
  addPolygons(fillColor = ~colors(district),weight =  1, group = "Districts") %>%
  addPolygons(label = ~NAME_ASCI,weight =  1, group = "Names", fillColor = "Grey") %>%
  addLayersControl(baseGroups = "CartoDB.Positron",overlayGroups = c("Districts", "Names"),position = "topleft") %>%
  addControl(html = "<input id="slide" type="range" min="0" max="1" step="0.1" value="0.5">") %>%   # Add Slider
  htmlwidgets::onRender("function(el,x,data){
                     var map = this;
                     var evthandler = function(e){
                        var layers = map.layerManager.getVisibleGroups();
                        Object.keys(layer).forEach(function(el){
                             layer[el]._container.style.opacity = +e.target.value;
                             });
                     };
              $('#slide').on('mousemove',L.DomEvent.stopPropagation);
              $('#slide').on('input', evthandler)}
          ")