Open certain channels and you hit a wall: 「This content is classified as sensitive and cannot be displayed」, with everything blurred out. As an adult user you can turn this filter off yourself, but here is the catch: on iPhone that switch does not appear inside the app at all.
Quick answer (2026): On iPhone (iOS), App Store policy keeps the 「Disable filtering」 switch hidden inside the app, so you have to turn it on at Telegram Web (web.telegram.org). Enable it once on the web and it syncs automatically to every device, iPhone included. On Android, you can switch it off directly in the app under Settings → Privacy and Security. After changing it on the web, fully close and reopen the Telegram app on your phone for it to take effect. (Per each platform's settings, verified 2026-07.)