If you show the peak areas graph ("View > Peak Areas > Replicate Comparison"), you can right-click on the peak areas graph and choose "Normalize To > Ratio to Heavy".
When you do that on the peak areas graph, it will also change what is displayed in the Targets tree.

The behavior of this changed slightly in Skyline 21.2, because we were fixing some weirdness in the behavior of using the "Ratios to" right-click menu item on the Targets tree, and the "Normalize to" menu item on the Peak Areas graph.
The net effect of that seems to be that, by default, Skyline does not display a ratio in the Targets tree.
If you had more than one option for what ratio to display (for instance, if you had both heavy peptides and global standards), then there would be a "Ratios to" menu item on the Targets tree right-click menu. But, if all you have are heavy peptides, that menu item does not get shown, and the only way to turn on ratios in the Targets tree is to right-click on the Peak Areas graph.

-- Nick