Please, please, PLEASE add an error check in the Events editor that complains if the developer fails to select an option for mouse button (and add a No Mouse option to the list to keep tablet/phone people happy). I have driven myself NUTS by adding an Event condition and forgetting to select a mouse button. Sure, I’m a newbe to Gdevelop, but I sure gained a lot of frustration and lost time tracking down that one little missing selection…
Thanks!
You want to rush and you end up losing time 
If no button is picked, it could mean “any button”. 
Maybe the phrase “Button to test” should be bigger, and/or the dropdown choices should appear automatically, or Left button would be picked by default…
I remember running into this issue too, when I first started.
I never thought this could have been a problem, but thanks for reporting it! Should be better now:
Hope it will be enough to avoid mistakes 
@4ian - you may need to rethink how to implemented the error check - I just updated to 5.0.0 Beta69 and I can still create “Mouse button pressed or touch held” and “Mouse button released” without specifying a mouse button.
Mac version of Gdevelop.
I also noticed that in my version of Gdevelop for the Mouse Events area, the layout is very different:
@4ian Would not be possible to set the left mouse button as default?
I have just tried and see if at least touch is working if no mouse button is selected and no touch doesn’t work neither. So I think it would be ok to set left mouse button as default or throw an ugly error in to my face. Sometime, gentle and elegant solutions like that tiny red error message below the field is just not good enough, need to be a little nasty to draw some attention 
Or should not allow the user to be able to add the condition without choosing a button.
I’m adding this kind of error display: 
Should make things very obvious
