Updated: Jun 23, 2021
In October 2020 Adobe officially released Lightroom Classic 10.0, a Lightroom Classic upgrade which removed the familiar Split Toning panel and replaced it with a new panel called Colour Grading. Instead of the familiar sliders which allowed you to add tones to the highlight and shadow areas of your images, you now have colour wheels which allow you to color the tone of shadows, highlights and, additionally, midtones, independently. The Colour Grading tool also has controls for blending and balance.
Take your images to new creative heights by adjusting the color wheels in any combination to create subtle, vivid, complementary, or contrasting looks (Adobe Feature Summary)
For a comprehensive starter guide to the new Colour Grading panel, check out this video from photographer Mark Denney:
I enhanced the colours of one of my images, similar to that used in the video, using the Colour Grading tool instead of the HSL panel. See before and after images below.
Below is an image from my phone camera. The first image is straight out of camera
In the second image some experimenting with Colour Grading produced a warmer tone
In the third image I simply adjusted the midtones
The tool gives plenty of creative control over colour enhancement although it could easily be overdone. Despite this, with some more practise and experimentation I can see greater use for this tool than for its predecessor, Split Toning.
Adobe provides a step by step guide to the Colour Grading tool here