7i76e what am I doing wrong

in an editor

(you must run the editor as root to be able to write the interfaces file)

basically
cd /etc/network
sudo EDITOR interfaces

where EDITOR is gedit, mousepad, nano etc etc

looks I will have to get back to it later.

I just installed linux mint 19.3 and I seem to have a connection now . I get a reply when I ping 10.10.10.10.
When I do the mesaflash --device 7i76e -- addr --10.10.10.10 --readhmid command in terminal I get the expected response . So now I know my board is ok.
This also means I have some weird conflict in Debian Buster correct?
Will I be better off just running Linux Mint instead?

is there much benefit to using mint 20 over the 19.3 ?

tommylight: his Ethernet was detected:

2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether f8:b1:56:bc:20:0f brd ff:ff:ff:ff:ff:ff
inet6 fe80::fab1:56ff:febc:200f/64 scope link
valid_lft forever preferred_lft forever

But was never setup properly
(maybe because the Buster dist uses the very broken wicd rather than net manager)

I had replaced wicd with the
apt-get install network-manager network-manager-gnome
apt-get remove wicd wicd-gtk

as per instructions.

OK so Buster would have worked but there was still some host setup issue

it's always something. LOL. I have experienced it on multiple occasions that when something in Debian doesn't work when it should
it will work on Mint. I am pretty sure that can be chalked up to my lack of experience.

It is hard to tell what's going on when there maybe multiple issues
unless you have banged you head on them enough times before

I do agree Debian has a lot of sharp edges (I'm running Mint on my test hardware)