But plz do tell me an example of a “dual faith” that can exist without violating one belief from the other.

Two very common ones are Confucianism + Taoism + Mahayana Buddhism (optional) in China and Shinto + Mahayana Buddhism + Christianity (optional) in Japan. The first is rather entertaining, because Confucianism and Taoism often have opposite teachings (falling respectively on the ‘ascend to technocrat’ and ‘retvrn to monke’ ends of the political compass meme). And yet, for the majority of Chinese history, most people - or at least most people who left behind written records - were both Confucian and Taoist.

There are also various blends of religions in South Asia, including Sufism, Sikhism (both Islam + Hinduism), various schools of Hinduism + Buddhism, and Navayana Buddhism (Buddhism + Marxism). Mentioning these to fundamentalists of any of the pure religions is not recommended.

It really depends on who your friend is, and who they are trying to defenf against.

If the US ( or Russian / Chinese) government really wants to access an internet-connected device, they can do it; what app you are using doesn’t even matter. For example, most people use the default Google keyboard, which could be compromised.

If the concern is about local goons / employers / coworkers, then both Telegram and Signal are more than enough to stop them prying.

As for whether to use Signal or Telegram, Signal has end to end encryption enabled by default, while in Telegram you have to switch it on for each chat. On the other hand, Telegram has the best UI among messaging apps hands down.