Well, I actually managed to get the pc to work right. Now the usb drive FreeNAS is on is GPT and the main storage ssd is also GPT.
I still have a problem tho. I am following this guide and stuck at 8:36.
Everything works fine up until this point.
Although I found the correct Netmask in ipconfig, Im not sure what IP i can use there. How to check?
If i fill in the IP with the same one shown the browser freezes and my nas goes offline on the old or new IP. A reinstall and reformat of all of the drives on the nas is required