Google Hangouts is pretty great, so of course Google is discontinuing it. I always have email open anyway, so its very convenient to fire of a chat while I'm on desktop.

I've used Hangouts since it was Google talk and used xmpp. I used several different multi protocol programs to connect to Google talk, Microsoft messenger, ICQ at the same time. Things where different back then.

Now I try to get as many as possible to get away from at least Google and Facebook services.

Encryption only available for mobile chats, right? And "secret" chats won't be available for the desktop view.

All chats are encrypted to and from the client, but only secret chats are encrypted end to end. And yes, secret chats are only available on mobile.

https://telegram.org/faq#q-so-how-do-you-encrypt-data

The point of encryption is to protect content from third parties. TLS-like encryption where messages can be read by server, is not protecting the content this way, therefore, calling it encryption is misleading. When average user asks "is it encrypted?", they're not asking "Oh I totally get that the developers can access the content but is it safe from passive eavesdropping in the network backend?", they're asking "Can anyone else read the messages?", i.e. "Are they E2EE?". To which the answer is no.

This is unfortunately correct, but I still prefer Telegram to other chat clients.

I mean, given the Signal protocol, the alternative would be your messages being routed from your phone via your computer. And the average person's computer isn't on/awake/connected to wifi as often as their phone is, so that'd be a much spottier experience.