"Loop Cut and Slide in blender 2.80 beta? https://www.oreilly.com/library/view/learning-blender-a/9780133886283/ch06lev2sec21.html

Ctrl+R command exists, I have also found this command in Preferences.

But where is it and its panel in the general window? It seems all the screens and tutorials are too old
You can find this tools inside the Tool Shelf, in edit mode



Hope that helps.

Good Luck