Leaflet for R is linked to Leaflet.js 1.3.1 from 2018. Some of the updates in 1.7 (better mobile support) and 1.8 (accessibility) look potentially important. Leaflet 2.x is in the words and looks like a fairly significant upgrade.

Folium has updated to 1.9.3
Here is one of the commits that upgraded from 1.6.0 to 1.9.3 and a link to the upgrade issue:
python-visualization/folium@6006ece
here are the other Folium releases that have updated leaflet JS to 1.4, 1.5, and 1.6:
https://github.com/python-visualization/folium/releases/tag/v0.11.0
https://github.com/python-visualization/folium/releases/tag/v0.10.0
https://github.com/python-visualization/folium/releases/tag/v0.8.0

Thanks!