Has Channel CoinJoins already been added and implemented in Lightning? I read about it two years ago, but had since heard nothing about it.
If it's added, then Lightning is still not the first choice protocol for regular Bitcoin users to "mix" their coins. Many users choose to convert to Monero or use CoinJoin and mixers. Plus it's marketed that "fast, cheap transactions" is still the main value proposition for Lightning, not privacy.
You may be referring to this article: https://thebitcoinmanual.com/articles/lightning-coinjoins/
Splicing and rebalancing seem quite useful and can definitely add some extra privacy on top.
I first read about Splicing and CoinJoin in this site, https://lightningprivacy.com/en/channel-coinjoins
But the information in there is limited. We need more ELI-5 kind of write ups.