Here's the official changelog for the new version (20.8):
- Chat Folders: Organize chats using up to 10 Chat Folders. Chat Folders replaced the Unigram specific Chat Filters.
- Polls 2.0: Visible votes, multiple answers, and quiz mode.
- Quizzes 2.0: Add explanations that appear after users respond to a quiz question.
- Improved file sender: Reorder files (if not in album mode).
- Add a caption for every video or image in the media file sender.
- New media editor (beta) to crop, rotate, flip images and to draw on them.
- Videos are sent uncompressed by default.
- Buttons for rich text editing: Right click / tap and hold on Chat input > Formatting > Show formatting. Or go to Chat Settings > Typing.
- New built-in themes: Classic, Day, Dark and Night.
- Redesigned profile pages.
- Improved stickers, GIFs and emojis.
- Added categories to GIF selection: recently used, trending, and many more.
- Preview stickers and GIFs by tap/click and hold them.
- Many (!) new animated emoji!
- Get a random number from an animated dice by sending a dice emoji.
- Send a dart, basketball, or football for the chance of a bullseye/goal.
- Cache statistics visualized by a ring chart (Settings > Data and Storage > Storage Usage > Clear Cache).
- Message corners: Tweak the appearance of message bubbles in Settings.
- Use bots like QuizBot to create quizzes with multiple questions. See how much time you have left to answer a question.
- Create custom Chat Folders with flexible settings, or use default recommendations.
- Right click / tap and hold on a chat in your chat list to add it to a Chat Folder.
- Pin (different) chats in each Chat Folder.
- Folder sidebar: Display the Chat Folder menu on the left instead of on top.
- Statistics for big channels: growth and post performance.
- Copy a MTproto proxy configuration to the clipboard (right click / tap and hold > Copy Link).
- Automatically fill in MTproto proxy settings on login using clipboard data.
- Upload up to 2GB per file.
- Improved app memory management.
- Turn the display off if the light sensor is blocked while playing an audio.
- Many more bugfixes and improvements.
- Added a link to the mobile specific Telegram group for tips and news about Unigram Mobile.
You can grab Unigram Mobile Messenger UWP in the Store here. If you still have the original Unigram installed then that will work for a while too, possibly even a year or so, there's no hurry to change, other than to stay involved in an active project. There's also the original Telegram PWA, which still works fine in Edge, other than not having push notifications.