You need both sorting and grouping to make the star rating sorting much easier.
Set "Sorting" to "Difficulty" Set "Grouping" to "Difficulty"
And now you'll see the 10 difference folders on your right. Start from "0 star" to "10 stars" Inside, the difficulty will be sorted ascending.
"0 star" folder contains beatmaps from 0.00 to 0.49 star. "1 star" folder contains beatmaps from 0.50 to 1.49 stars. "2 stars" folder contains beatmaps from 1.50 to 2.49 stars. And so on...
If you want a specific range that is not included as a sorting option you can do something like this by typing it in the search bar in the song menu. Ex: "stars>=2.38 stars<=2.64" thatll show anything between 2.38 and 2.64 stars