I was under the impression that shadowbanning was a moderation technique reserved for the admins, and unavailable to subreddit moderators; IIRC, it also applied to the entire website.
Reveddit [1] or its accompanying extension [2] can alert you when this happens. I'm the author. You can see the behavior yourself on r/CantSayAnything [3] or read more in the FAQ [4].
[1] https://www.reveddit.com/about/
[2] https://www.reveddit.com/add-ons/direct/
So it's not a true shadowban, but any posts you make on subreddits who have shitlisted you will get deleted instantly.
And of course when a post of yours is deleted on reddit by a mod, reddit does not tell you this or indicate it to you in any way.
I've long since stopped caring about the ban itself, but I'd be lying if I said I wasn't curious to learn the reason for it!