Here's the official changelog, quite a bit of which is more for use in a modern Desktop browser like Chrome or Edge:
New
- Fleets: We’ve enabled DM Fleet previews and the Fleet viewer screen for all.
- Nudges: When Retweeting a Tweet that contains a link to an article, you’ll now be shown a nudge prompting you to think about reading the article before you share.
- Topics: There’s a new page for browsing and picking Topics. You can find it by going to the Topics screen via the More menu, and clicking “More Topics”. You can also navigate there directly via twitter.com/i/topics/picker.
- Topics: We’re experimenting with showing Topics to follow in the sidebar on widescreen views to give you more examples of Topics you may be interested in.
Updated
- Accessibility: Voiceover will now read out labels for government and state-affiliated media when focusing a Tweet that includes these labels.
- Accessibility: Improved focus navigation and voiceover when navigating into a Tweet within a conversation.
- Accessibility: Corrected accessibility markup on Buttons that act as links to other pages, or reposition you on the current page.
- Account: Improved readability of error messages on the account login page.
- DM: Improved dynamic display for larger numbers of avatars in the DM conversation information section for group conversations.
- Emoji: Updated emoji to Twemoji 13.0.2. Visual coverage of the changes can be found at Emojipedia, and more specific information can be found at GitHub.
- Lists: Added screen name to the add/remove from Lists menu action for additional context.
- Notifications: Increased the number of avatars that are shown for condensed notifications on the notification screen.
- Nudges: Improved the look and feel of article nudges shown at various screen sizes when Retweeting a Tweet with a link to an article.
Fixed
- Bookmarks: The floating compose button will now show properly on the Bookmarks screen on mobile clients.
- Composer: The cursor will now start at the beginning when auto populating the composer with a hashtag from an Event or other source.
- Composer: Opening scheduled or drafted Tweets from the inline composer will no longer display an empty composer modal.
- DM Drawer: The popover menus that are displayed for DM messages will no longer scroll with the body of the page when using the DM Drawer.
- DMs: Fixed an issue where the DM muted accounts timeline would show as empty after navigating away and back.
- DMs: When sending media through DMs, the composer will no longer incorrectly clear, and will become disabled until the media has actually sent.
- Events: Fixed issues with cropping on Event header images.
- Lists: The Lists menu item will no longer disappear at smaller screen heights.
- Lists: Corrected an issue where clicking on Followers on the List screen was showing an error screen.
- Lists: Fixed an issue where rapid presses of the next button when creating a List would create duplicates.
- Profile: We will no longer show the location icon if the location is empty.
- Scrollbars: Updated a number of places where scrollbars were being shown when they shouldn’t have been.
- Topics: Fixed an issue where clicking on Topics in the carousel was not requesting new items as needed.
- Topics: Unfollowing a Topic from within the home timeline will now correctly show a confirmation prompt.
- Tweets: You will no longer be able to trigger the modal for blocking via keyboard shortcut on your own Tweets.
- Tweets: We will now show the properly localized timezone on the Schedule Tweet page.
As ever, a few illustrative screenshots:
With display dpi set lower, the changes to the left-hand menu (always on with this display setting) become interesting; (right) the 'All Topics' view, note that double-tapping is the way to select a 'pill' under Windows 10 Mobile...
Good stuff. You can grab or update the Twitter PWA-ified UWP client here in the Store.
PS. As a reminder, this application now trumps third party options like Tweetium UWP because of recent Twitter changes which knocked push notifications on the head. Along these lines, see also my (older) general round-up of ways to access Twitter under Windows 10 Mobile.
PPS. As for other social networks, Winsta handles Instagram well, while Likebook (et al) similarly handles Facebook.