Twitter admits it can “downrank accounts”, which is a modified from of shadow banning.
As I have noted, a shadow ban can mean only the poster sees their tweets, or only their current followers see their tweets – but their tweets may be displayed less frequently to their followers, or not at all to non followers – thereby making the tweets disappear from search results. That this goes on is apparent due to other oddities, like messages from Twitter saying a Tweet is unavailable, but when you click through, you can see the tweet that is “not available”.
A problem with secret censorship is the censor is eventually discovered.
As of 1 pm, PST, a search of Google News shows that not a single mainstream news outlet has reported on current or former Twitter employees admitting on camera to shadow banning tweets and users whose political messages they disagree with.
Update: Twitter is not denying that it engages in various forms of censorship. Twitter does say that it has privacy and other policies in effect. While denying it does shadow bans, it does acknowledge down ranking, which is a variation of shadow banning.