It seems you've done a good job of troubleshooting so far, and the issue appears to be specific to your desktop computer and the Battle.net platform. Let's explore some additional steps to help identify the problem:
Check for background processes: Make sure there are no other applications or processes consuming your internet bandwidth while you download Black Ops 4. Check the Task Manager (Windows) or Activity Monitor (macOS) for any unusual network activity.
Firewall or antivirus interference: Check if your firewall or antivirus software is affecting the download speed. Temporarily disable them and see if there's any improvement in the download speed.
Proxy or VPN settings: Verify that you are not using any proxy or VPN settings that might be affecting your download speed.
Battle.net server location: Battle.net might have different server locations, and it's possible that your desktop is connecting to a distant server, resulting in slower speeds. Check if you can manually select a different server location within the Battle.net client.
Check MTU settings: Maximum Transmission Unit (MTU) is a network parameter that can affect download speeds. You can try adjusting the MTU settings on your desktop to see if it makes a difference. Typically, the default value works fine, but in some cases, tweaking it can help.
Flush DNS cache: Open the command prompt (Windows) or terminal (macOS) and enter the command "ipconfig /flushdns" (Windows) or "sudo dscacheutil -flushcache" (macOS) to clear the DNS cache, which might help resolve any DNS-related issues.
Check for Windows updates: Ensure that your desktop has all the latest Windows updates installed, as these updates can sometimes improve network performance.
Contact Battle.net support: If the issue persists, it's possible that there might be a server-side issue or a problem specific to your Battle.net account. Reach out to Battle.net support for further assistance.
Consider network adapter issues: While you mentioned that all drivers are downloaded, there still might be a network adapter-related issue on your desktop. Try updating the network adapter drivers or even reinstalling them to be sure.
Perform a traceroute: Running a traceroute to the Battle.net servers can give you insights into the network path and any potential bottlenecks. It might be helpful to see if there are any issues with the routing.
Temporary network congestion: Even if it's not a general network congestion issue, there could be temporary congestion between your desktop and the Battle.net servers. You might want to try downloading at different times to see if the speeds improve.