Title says it all really…
For new accounts it can be. I think moderators are supposed to check them and approve them to make sure you’re a genuine account. I think it’s trigger based, and if you trip the trigger it can get flagged (like your first post linking to an external website, for example)
It can happen to long standing users at times too, for seemingly no reason. I still have some posts on here that are pending review from months ago.
Your first post has to be approved before it goes live.
But this isn’t where you should be asking for help really. People here will definitely help, but it isn’t a support forum.
In the app, got to the help section, search “contact” and press “contact us” and then you can speak to Monzo.