Yes, you are right. This is a browser limitation but when you add your web app to your home screen on your mobile, the application goes fullscreen right away when requested through code. Well, it's the expected behaviour.
Yes, it's true, when you build your app and run it as a normal mobile application, everything works great. But an advantage of Construct(2/3) is the opportunity to preview your project without compiling/wrapping within a native mobile application.
So we are back at the original problem: When using C3 preview on mobile, requesting fullscreen at start of layout doesn't work. But when previewing on mobile from C2, requesting fullscreen at start of layout do work. I did some test with a barebone capx in C2 and C3 and here are the results:
iPhone/Nexus5 - C3:
iPhone C3 Preview Screenshot
Nexus5 C3 Preview Screenshot
iPhone/Nexus5 - C2:
iPhone C2 Preview Screenshot
Nexus5 C2 Preview Screenshot
Please note that both file contains exactly the same code and have exactly the same settings.
There is a difference between C2 and C3 previewing results.
Now, how can we solve this? is it possible with C3 right now? Do I have to report this as a bug?
Thanks you dop2000 for your help by the way. I appreciate it.