That's a system put in place against the legal system but it's not a technical limitation. For example, he will be able to look into the chats of his ex without

That's a system put in place against the legal system but it's not a technical limitation. For example, he will be able to look into the chats of his ex without the need of court orders of multiple unfriendly countries proving that the situation is grave and universal one. When the limitation is not technical, your only guarantee is the integrity of the operators and the lack of interest of your attackers coercing the operators into spying on you. In Telegram's case one could easily assume that the Russians and now the French said him "Nice fortune you built, you are very successful person with a long life to live ahead. It would be a shame if you lose your fortune or spent your days locked in a room instead of flying on a private jet to Ibiza"