As a replacement for the Split Toning panel, the Color Grading panel allows one to apply a color tint to shadows, highlights, and/or midtones, as well as globally to the entire image, using industry standard three-way color controls (i.e. with hue, saturation and luminance controls).
Replicating Split Toning
To completely replicate the old split toning capability, use the Shadows and Highlights tints, Balance slider, and set Blending to 100.
Still Seeing the Split Toning Panel?
If you have updated to Lightroom Classic 10 and for an image you see the Split Toning panel rather than the Color Grading panel, your image is still in an old process version – it must use 3 or later to leverage color grading. To update your image, click on the lightning bolt below the histogram.
There are three new presets in the Creative section of the Presets panel that use color grading: Cool Matte, Cool Shadows and Warm Highlights, and Warm and Moody. Other presets that used to use split toning have been translated to color grading (with Blending=100).