This method is direct and simple, just follow the screenshots below to view 18+ contents.

Note: Some users might not have this option in the settings. Try method 2 if method 1 is not available for you.

Settings > Chat Settings > Show 18+ Content

This method will require you to login to your Telegram on a mobile or desktop web browser (not app). 

*You can try to do the same settings on your app, but many users claimed that it is not working.

Settings > Privacy and Security > Turn on Disable filtering

This will require you to install Telegram's official app on your desktop.

Windows = https://desktop.telegram.org/
macOS = https://desktop.telegram.org/

Settings > Chat Settings > Show 18+ Content

If you do not see the show 18+ content option, use the method below (turn on disable filtering).

Settings > Privacy and Security > Turn on Disable filtering

Log in to your Telegram via the web browser version at https://web.telegram.org/

This can be done on both desktop and mobile. Be sure to stay logged in to avoid going through the process of re-logging in (optional).

*** Make sure to disable Telegram's filtering that hides sensitive content. Go to Settings > Privacy and Security