If you do a search of shadow banning, you'll find sites that claim to help you identify whether Twitter or Instagram has shadow banned your account. The basic idea of shadow banning is to spoof the shadow-banned user into believing their public posts are visible to all while in reality the posts are visible only to the user or in some cases to the users' followers.

Wikipedia's definition of shadow banning is:

"Shadow banning (also called stealth banning, ghost banning or comment ghosting) is the act of blocking or partially blocking a user or their content from an online community such that it will not be readily apparent to the user that they have been banned."

Here is whatis.com's description: "Shadow banning is controversial because it allows an administrator or moderator to effectively become a censor and prevent specific users from interacting with other members of an online community on an equal basis."