Actually it does diagrams, sequence and flowchart.
Sadly, the app has gotten more or less no development for at least 4 years and the developer has stopped responding to bug reports for at least a year. It's abandonware at this point.
Thanks for the correction! I used to use it too (I use Obsidian [1] now). Also sorry it hasn't been updated. I kind of felt that while powerful, it was also too complicated some times.