For all of the much-vaunted complains about their lack of it, I am not aware of any proof or credible claims that Telegram the company has ever revealed the contents of non-encrypted messages or group chats.
Meanwhile, I don't think any authorities actually care about to what extent E2E Encryption makes it harder for Signal the corporation to extract message data. There's plenty of other ways to skin that cat - on-device compromises, abuse of backup mechanisms, abuse of mechanisms to manage linked devices, etc. They'd go after them just the same if they thought there was anything they really wanted on there.
If there's any real difference, I think it's most likely because many more of the group chats that such authorities are aware of and find "interesting" are on Telegram because basically nobody really does E2E well in medium-large groups right now.
Famously, Signal complies with court orders by giving up all the data that's requested that it has, which isn't very much. This is what you expect from E2EE platforms.
A court order to do the impossible is invalid. Telegram gets in trouble because it's possible for them to comply but they choose not to. Subpoenas are usually worded as "you must provide all information you have, relating to ..."
Meanwhile, if you believe that any Governments actually refrain from prosecuting Signal executives due to their refusal and/or inability to produce the messages from private chats because they have E2EE, well, I've got a nice bridge to sell you.
If they actually are refraining from going after Signal executives in a similar fashion, most likely either 1. Nobody is actually using it for anything interesting, 2. They are actually secretly cooperating somehow, or 3. Governments are already happy with other technical means of extracting the contents of Signal chats they are interested in. See the US FBI's curious sudden lack of interest in Apple's ability, or lack thereof, to extract a wanted suspect's iMessage messages.
Pavel Durov was arrested when he traveled to France because Telegram was noncompliant with French court orders. You can ignore them in Russia... you can't ignore them in France. And you can ignore Russian court orders in France but not in Russia. And the Russian or Indian court is free to ask the Montenegrin government to suspend your domain name and the Montenegrin government is free to agree or disagree.
https://edition.cnn.com/2025/03/24/politics/yemen-strikes-jo...
and it didn't leak because of Signal's security, but because an Atlantic maganize journalist was added to the group chat by Waltz.