What is SegWit2x?
SegWit2x was a proposal for upgrading Bitcoin block sizes. It was never implemented due to the Bitcoin developer community failing to reach a consensus on it.
SegWit2x was a follow up to the SegWit, which reorganised how verification signatures were stored on blockchain data. SegWit2x proposed increasing block sizes from their current size to allow more transactions to be processed. However, there were concerns this could slow down the network due to the increase in processed transaction data and the proposal failed.
SegWit2x would also have required a hard fork for the Bitcoin blockchain. This essentially means the original Bitcoin chain would have to adapt to the new block sizes, which would have required miners to adapt to the change, potentially leading to a new chain as seen in the case of Bitcoin Cash.
Hard forks are considered drastic proposals as they require the trust that has been built for the old chain to carry over to the new version, which can lead to user bases breaking up. A real world parallel is political or religious groups disagreeing on their ideology or practices, leading to the formation of new denominations that split from the original group.
SegWit, by contrast, was a soft fork rather than a hard one. Soft forks differ in the sense that although they change the rules for how the network operates, they are backwards compatible with all previous transactions that used the old rules, making them more likely to pass if the proposal offers needed improvements to the protocol.