I ask myself or you if it has any advantage to keep the previous Xbox, namely the Xbox One X when you have the new Xbox, Xbox Series X. Should I keep the previous one? Are there any arguments against selling the predecessor?
If you take a look at eBay, you will see that you hardly get anything for the old Xbox. Therefore, it is better to keep it for games that you want to play again or for the collection. Otherwise nothing speaks against the sale. Only in terms of value, that's not much and rather tough until it is sold