When I right click on the shortcut there was an option to "Troubleshoot compatibility". Just leaving this here for future reference: TLDR: Try cutting off internet during Outlook startup. Thanks Michael, cutting the internet off first and then adjusting the settings worked well for the MS Office Outlook 2016 Pro Plus. Then Outlook opened fine and created its own new OST file. I deleted my second accound and outlook starts up fine.
I used Process Monitor to see what Outlook was actually doing in my case when it is stuck on loading the profile. It was somewhat annoying to just watch the screen hanging on profile loading screen. You know you could hold CTRL in and right click the Outlook-icon in systray to see that TCP-traffic? Outlook only works with one account For our situation we're 365 subscribers using Office 2016 on Win7 SP1 inside a VPN environment with Exchange Server 2013. In the list of available options, click to select the Disable hardware graphics acceleration check box.
I saw a bunch of Telemetry and TCP related stuff which made me think it is trying to connect somewhere but does not succeed. I have a customer now on the phone and it seems it's resyncronizing the OST-file before loading Outlook. The loading Profile window comes up and tried to load. Opening in Safe Mode allowed me to get Outlook open, then I disabled all but 2 add-ons (Skype Meetings and Exchange 2013).
Disabling all network interfaces during startup of Outlook immediately solved my problem. it started suddenly and I could not get Outlook to run even in safe mode. Has Scan PST maybe been moved to run pre-startup of Outlook 2016? I disabled everything related to Share Point, Social Media, and One Note (who uses that? After disabling the plugins Outlook would open normally.
WORKING SOLUTION: ---------------------- Disable the following network adapters: Microsoft Loopback Adapter Npcap Loopback Adapter After this, outlook would open within 5 seconds and not hang on loading profile anymore.