Meanwhile for data centre usage, what is the attraction for faster copper vs fibre interconnects?
40GbE with cards and DAC cables are pretty cheap if you can get them shipped from the states. Cards are on the order of 15-50 (for both 10GbE to 40GbE QSFP).
If you are trying to figure this stuff out on your own from listings, you will be utterly lost. Use a big llm to help you out and cross reference, stuff can get tricky real quick.
If you want to get started, the lowest friction path is to get a couple intel 520, 540 or 710 nics and some patch cables. I started with just two 520s and a some cables for loop back.
A little bit more than the states, but not bad. https://www.ebay.com.au/itm/394258109292
https://hackaday.com/2023/10/24/using-industrial-ct-to-exami...
https://www.lumafield.com/article/usb-c-cable-charger-head-t...
That's not exciting for consumers, 10g hasn't managed to get far for consumers, although 2.5g is starting to show up more places. I'd rather not buy from aliexpress, but there's some ok priced stuff there than can do 2.5g with maybe a 10g port or two.
10BaseT1L is also mentioned, but that's 10Megabit on a single pair, not exciting for speed, but maybe exciting for reusing limited wiring that's in place.