Hello and welcome to the Fediverse.
Telegram's secret chat's encryption algorithm is made by Telegram themselves, which is already a red flag. You generally don't want to roll out your own encryption algorithm if you aren't cryptographers, which Telegram people aren't. Their MTProto is also not proven, so you'd rather not want to use it.
Here's a blog entry about their MTProto: https://web.archive.org/web/20180420061726/http://unhandledexpression.com/2013/12/17/telegram-stand-back-we-know-maths/
As an instance admin, you can see who voted what. Moderators are also able to view votes in their community. See discussion regarding vote privacy here: https://github.com/LemmyNet/lemmy/issues/4967