Hey there Infinitiive! Thank you for taking the time to reach out with those details. Can you temporarily test an alternate network such as a mobile hotspot or VPN? This will help us quickly determine whether the installation issues are network-related, since you mentioned this being a new PC.
If the game installations proceed as normal when using an alternate network, at that point we can be sure that the issue is isolated to the primary network. In these situations, ultimately we can only recommend contacting the Internet Service Provider (ISP) for assistance determining what is causing the issue to occur on that specific network. They might need to adjust network-level security/firewall settings on your modem or temporarily replace the device to narrow it down further. I always recommend requesting to be forwarded to a “level 2 or level 3 technician” when contacting the ISP since the front-line representatives typically only have access to basic diagnostics and troubleshooting tools.
I hope this helps you get in-game smoothly! Let us know if you have any questions going forward.