It should be know that there is an unofficial Telegram client, Unigram, that can run on every Windows 10 device (PC, Xbox One, Holo Lens and Surface Hub) and, in particular, supports E2E Encryption. The project is open source so Telegram could easily implement Unigram's features in Telegram official client: https://github.com/UnigramDev/Unigram
Mario
This is the list with all the suggestion cards regarding how to improve E2E-Encryption implementation in Telegram, make sure you vote and share them :)
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Secret Chats and Groups on every app and device supported by Telegram (Android, iPhone / iPad, PC / Linux, macOS, Web/ browser): Secret Chats and Groups on every app and device... #8631
Make Secret Chats and Group Messages Synchronized and implement a Back-Up option: Make secret chats and group messages synchroniz... #8307
Secret Group Chats: Secret group chats #1231
E2E Encryption for Saved Messages: e2e encryption for saved messages #2264
Implement Secret Channels: Implement Secret Channels #8707
Implement Secret Bot Chats: Implement Secret Bot Chats #9229