@george1421
Thanks for the feedback.
We switched to Dell from another brand, so we don’t have any adapters laying around, but i have a Dell DA200 USB C dongle with ethernet at home, good idea to try that, i’ll bring it tomorrow just to test! 
I quickly tried some version of Ubuntu live ( i think 18.04) on it and it worked that time last week. But i downloaded Debian Buster now and tried as well just to make sure as much as possible, it’s the same problem there now! Only on one of the PC’s, Debian Buster on “the first” PC of the same model continues to work fine with the same cables & BIOS here as well… Thanks for pushing me to actually double check that again!
I got to DOA submit this PC to Dell soon, but unsure how they’ll see this as it’s working in Windows, but i’ll hope they have enough goodwill with us being a new Dell customer with a big order going in.
Before doing that, i’m reinstalling windows 10 manually now from USB / Win 10 media creator just to make sure that works still or now.
Btw, we began our environment change focused on the 3060, then the 3070 came and we were preparing purchasing of that model, but we slowly trickled into optimizing our physical environment with the 7070 Ultra instead and landed on this model to purchase now. It’s quite different from 3060/3070 since it’s built on laptop parts to begin with. It’s still quite expandable and configurable, but no full size PCI-e etc 
UPDATE
After talking with a Dell tech who helped me brainstorm a few things and we doublechecked the revision of the NIC, which is the same on both/all machines (Rev 11 of the I219-LM Intel ethernet NIC), we didn’t get any wiser, so basically still at the same spot.
What i’m concluding is that it seems to work on newest Kernels even on this troubling PC, so i’m leaning to have to build my own kernel and it should sort itself out (what i’d probably had done by now, if it weren’t for all the other PC’s already working…)