I would like to use the short keys on mac for opening a diagram from a collapsed process diagram like I do it on windows (ctrl + click on "+" in subtask). Is there any other button I shall try or is it not yet supported?
This short key doesn't work for MacOS. In this case you'll have to click on "+" in the collapsed task and then "Open" above, so you can reach your diagram with 2 clicks.
The most shortkeys for windows work with "command" instead of "control" for mac.
Below you have a list of short keys for windows which you can adapt for mac-os:
KBA , BPI-SIG-PM-MOD-EDT , Graphical Editor for SAP Signavio Process Manager , How To