Hey, thanks for your info! I tried it all, and figured something else out.
First I have no firewalls, or anything like that. But when I start my computer and connect it to a different WIFI than my WIFI at home, it works perfectly. After connecting to any other WIFI, I can use my WIFI at home as well, it just can not be the "first" wifi to be connected to my computer, which is super weird.
I now start my computer with my iPhone Hotspot and after that switch to the WIFI, then it works perfectly?!?!