It was me that set the subnet mask 188.8.131.52. This was not changed from being connected to the school network. I cannot change ist to .0 as my router prompts "Out of range, please adjust start IP address or user's numbers.". Also, I do not think thats the problem because its the same setting for my other hosts.
There are no DNS servers set in the IPv4 properties of my network adapters, everything is empty.
IPv6 is still enabled.
I tried to set the gateways IP as a static DNS server in the router, but that doesnt change a thing.
Here's a picture of the routers config.