A question about relays and clients 😁

So basically I wanted to ask do clients get to choose what users can see from relays based on what they (the clients) want to show? Like for instance I tried entering a few relays into different clients like (wss://nostr.bolt.fun) on Snort, Iris and Blogstack, but couldn’t see anything like posts or stuff, and when I tried sending a post from Blogstack to it, it didn’t work…Just a bit confused as to how it works, is it that some clients can’t see what others post or…?