They never were and never advertised as such. There’s secret chat’s that only work from the originating device to the receiving device that are e2e.
Group chats were never encrypted because they’re convenience chats, not places to tell secrets. IE you can look back at all the history and shared files from any device you log into. You can search for a message from 2 years ago to remember something that was discussed previously.
I’m a big telegram defender because it’s the nicest cross platform chat app to stop your parents from creating the n+1th mms group chat from their iphones, torturing all android users. It’s also not a Meta app, and doesn’t have the nerd requirements of an actual encrypted chat.
I use it for work and I find it clunky and an overall mid messaging experience. It feels like groupme from 7 years ago. I know the “nothing to hide trope” is shit, but sometimes you actually are saying little of substance and you want a nice user experience day-to-day rather than sacrifice features and UX for a privacy boogieman.