You can check by trying to visit their user page. If it 404s, they're shadowbanned. The shadowbanning system is terrible. It's not transparent, it just randomly censors people, some of whom happen to be spam, does not notify the people involved and offers no recourse to those who have been shadowbanned. I was shadowbanned a few years ago, I spent about 3 months spamming different reddit contacts, then one day noticed I was unshadowbanned.