Why is the rectangle tool missing from DxO PhotoLab ?

The rectangle tool is one of the features included with ViewPoint, which is no longer included as part of DxO PhotoLab.

To get perspective correction tools, we recommend that you purchase ViewPoint 3, which is available as a powerful standalone program and as a plugin to DxO PhotoLab.

If you're currently using DxO OpticsPro 9, you can also upgrade to PhotoLab, which includes ViewPoint 1 free as a plugin.