2020 iMac 5k - 10G ethernet not working

I've recently started to want to use my WIRED ethernet on my 2020 iMac 5k. for the past 4+ years, I've been just fine with wireless, but I've decided to updated/upgrade my home intranet (hardware), updating my switch from an 8 port gb switch (unmanaged) to a 16 port 2.5gb switch (unmanaged), and all my cat5/5e/6 cabling to cat8 braided. I also updated my wifi/router from an service provider/OEM single/standalone modem/router to a wifi7 quad frequency 3 node mesh system.

I'm finding that with both my old network, and my new network setup, I cannot get the iMac 5k wired ethernet to properly work.

hardware tests all show the 10g ethernet is functioning properly. terminal ifconfig en0 shows it properly negoationed (after reboot), an IP address in the correct range by the router, as well as the 2.5gb limit of the switch. the old switch hardware also produced similar results ... a 1gb limit auto-negotiated as shown w/ifconfig en0. The network (again) after a reboot), shows the Ethernet Connection as "active" (green). within the Router software, I see that connection as OFFLINE (so somebody's lying).

if I deactivate the ethernet, then reactivate it, network will ALWAYS go to self-assigned IP (orange color) with a 169.x.x.x address. Only a reboot of the iMac will get the network connection back to Green/Active.

I've tried changing the service order (when it's first, no internet/intranet works). When WiFi is first, everything internet/intranet works.

I've tried deleting then re-adding the service back multiple times.

I've tried setting a static IP (manual) making sure on the router that IP isn't being used.

I've tried inactivating the network Wifi and just using (when green) the active 10g ethernet.

I'm privy to many of the google searches regarding this issue, and frustrations others have expressed on this forum, macrumors, and other forums.

This 10G ethernet should be plug and play.

I will (in a couple weeks) have access to a windows 10g ethernet laptop ... will update this post with the testing results ... I'll test using the same cable/connection to see if there's any issues / problems with this (this will rule out my network as the culprit, which I'm absolutely sure isn't the problem given I've tested on a brand new network/setup).

Tried some things like no VPN (deleted), privacy turned off, etc. I guess I could install the originally provided OS to see if it works ... maybe some weekend when time permits ...

MacOS 15.1

2020 iMac 5k / 128gb / 8tb

I'll be updating w/more testing and images as I proceed through this issue