Lightroom doesn’t appear to offer native hotkeys for directly switching crop aspect ratios. Based on the community answer, a practical workaround on Mac is to use a macro utility such as Keyboard Maestro. It can automate GUI actions like opening menus, selecting crop ratio options, and performing repetitive interface steps from a keyboard shortcut.

This won’t add true Lightroom-native crop-ratio shortcuts, but it can speed up your workflow by simulating the mouse/menu actions you’d otherwise do manually. If your crop edits are still being made inside Lightroom, compatibility with Lightroom/Photoshop and XMP sidecar metadata should remain intact because the edits are stored by Lightroom as usual.

So: yes, a tool exists as a workaround—use a keyboard macro app rather than expecting Lightroom itself to provide those ratio hotkeys.