@Crashon
Tried clearing the Arp Cache - this sadly did not change a thing.
And like i said before, im almost 100% sure my router or its settings aren't the problem and just to make it clear: Im not using a Wi-Fi connection!
@TUNANKA
I did another complete and fresh install, following your steps (just to be sure, even though im pretty sure its the exact same thing i did before ;)) - to no avail.
As you can see in my answer above: My connection or my ISP in general are not even close to being a problem over here. Got a stable and superfast connection! Couldn't be happier!
I also already tried shutting down my Anti-Virus/Firewall and/or adding basically any kind of exception you could think of.
@iFlufy
As far as i understand, not being able to properly connect to the API,resulting in me not loading the server list is the problem. -> Not my inability to enter my Login Data, i.e. my email adress or password.
Nonetheless thank you for you detailed post buddy :).
@ChinosMasta
Not using a VPN
They are automatic
Reset my modem like 12 times already
Did two full reinstalls so far, but maybe ill give it a third try
Not running any beta version and im pretty sure the launcher would've told me the second i opened it. Double checked on Steam just to be sure though
@Dark Haus
Giving a few things another shot atm, will open up a ticket if everything else fails.
ANOTHER SCREENSHOT: https://imgur.com/a/UVy71
This is what the menu looks like after entering my data and hitting "Login"