Windows 10 workstation refuses to do a DNS lookup after NIC card upgrade

Old workstation was getting intermittent disconnects on its decade-old onboard NIC, so I installed a new PCI NIC, which was working great at first, but suddenly Windows now refuses to do a DNS lookup.

This workstation runs some developer services and is assigned a static IP by the router.

After a week or so of working fine, Windows complained today because the static IP address was already used on the old network adapter. So, I made sure they were both set to DHCP, de-allocated the old MAC on the router, and allocated the new one to the same static IP.

The workstation has full connectivity to the LAN, I can even SSH to another host and make a request out to the Internet from there.

Every other machine on my LAN can get to the Internet just fine.

If I ping a WAN IP address directly, Windows is okay with that.

If I look up a domain on the command line with nslookup, that works, too.

But if I try to actually pull up google.com or whatever in my browser, or ping it by domain name instead of by IP address, OR use the PowerShell Dns lookup utility, all I get is timeouts and errors.

I've flushed my DNS cache, I've done a full network reset which uninstalls and reinstalls all network adapters to factory defaults, I've even rebooted into safe mode to see if that made a difference. I've restarted the desktop itself and the router a good half-a-dozen times now.

I'm also quite baffled that nslookup works fine whichever DNS server I pass as the second argument, but opening PowerShell and trying the same domain and server with Resolve-D sName or [System.Net.Dns]::GetHostEntry() give me timeout errors.

What is going on?? I've never encountered this situation before. Windows configures its default DNS on this adapter to 192.168.1.254, which is the router, but if I force it to use 8.8.8.8 or other public DNS, it doesn't make a difference.