From other programs, I'm used to something like `Ctrl`+`Alt`+`Shift`+`C`/`M` or similar.

[![screenshot](https://i.stack.imgur.com/jNv1z.png)](https://i.stack.imgur.com/jNv1z.png)

Edit: Apparently it is also not possible to define custom shortcuts in PowerPoint? Please correct me if this is wrong/outdated info.