According to the release notes for the update, it includes Touch Bar options for switching tabs and searching when the main window is in focus along with new buttons when using the composer to create a tweet or viewing a user's profile page.
Twitter's full release notes for the update are below:
We made a number of improvements to Twitter. A few highlights specific to Twitter for Mac:Twitter released this new version of Twitter for Mac back in October, when macOS Catalina came out. macOS Catalina was built using Apple's Catalyst feature that allows iPad apps to be ported over to the Mac.
Fixed: App freezes for text input or delete with certain languages such as Chinese
- Improvement: added buttons to switch tabs to touch bar when main app window is in focus
- Improvement: added search button to touch bar when main app window is in focus
- Improvement: added more buttons to touch bar when composer is in focus
- Improvement: added more buttons to touch bar when viewing a user's profile page
Catalyst allowed Twitter to re-release Twitter for Mac, which it had previously discontinued early in 2018. The Twitter for Mac app offers a design and capabilities similar to the iPhone and iPad apps, but with Mac-specific tweaks such as Touch Bar support.