I’ve seen it firsthand how some channels are not available on telegram downloaded from app store vs direct apk download
the right word is “visible”… discoverability on Telegram has always being broken, as in you search for a channel, good luck finding it!.. like you said it’s because of your phone number region… Etc… that has been fixed when they introduced similar channels feature, since then I never used that broken search functionality… But once you find and join a channel, if Telegram mods decided to censor some posts or remove the entire channel, it’ll be removed from all clients… unless there is some client out there who saves snapshots of all channels or posts ( somehow )