@Unlucky_Alf 

Deco X50 has gigabit Ethernet ports. If you need short Ethernet cable, it should be Cat 5E or Cat 6. Note letter 'E' in '5E,' it is important: Cat 5 cable (without 'E') may not get you gigabit link speed.

Also, do not buy Cat 7 and up cables- their specs are better on paper, but depending on supplier you might get cable that is not up to standards. Cat 5E and Cat 6 are older and often made from better quality materials. If you have nearby store that sells surplus electronics and cables, check there for Cat 5E or Cat 6. They should be inexpensive and from those available choose one that looks more sturdy.

As for hardware version of Deco, see this TP-Link FAQ: https://www.tp-link.com/en/support/faq/46/

You can find hardware version printed on label attached to Deco unit and on box Deco came with.