1. HOW CAN I DO A BACKUP of those amounts of assets that I have information on Ledger Nano X?
You would simply initialise the Nano S using the 24 word seed mnemonic that you got when you setup the Nano X. Basically, during setup of the Nano S, you would click the "X" button when it asks if you want to "configure as a new device":
It will then ask you to enter your 24 words. Once this is complete, the Nano S will essentially be a "clone" of the Nano X and allow you to access the same wallets/addresses/assets etc.
2. What is a purpose of doing this backup if anyway I can have a recovery phrase so I can restore it in ANY case? I would simply buy another new wallet and restore it, so what is the purpose of having a backup wallet?
It's just handy to have... it isn't necessary per se. As you've already stated, with the recover phrase you can restore into another BIP39 wallet or buy a replacement wallet. However, you might like to have ready access to a spare device in case you need to access in a hurry and the X is damaged/stolen/lost etc... being able to restore immediately to an S is a lot safer than restoring to a software wallet and is a lot more convenient than waiting for delivery of another wallet.