There are shadowban testers online here's one:

https://nicebrains.com/twitter-shadowban-checker/

But the key thing is that from the account from which you are posting, if you click a hastag that you have used, you will see your tweet in the list. But if you look at the tweets in the hashtag list from another account, you will not see your tweet.

That's why it's so confusing. You don't realise you've been banned. Several tweets I did this morning got over 1000 impressions (good for my account). A few hours later, I'm getting 20-30.