The new features are listed in the e-mail announcing the beta availability in Test Flight. They are also listed in the Test Flight app.
This is what the latest notification states:
This build: Adds some polish around Loop Beat Knob and adds new propagate feature (see below). Hello and welcome to 2022!!! Version 2.300 is a massive, gigantic, huge leap. 1. Ableton Link Integration. See mididesigner.com/qa/9067 (with video). Look-ahead, tempo-locked control loopers, finally! 2. Add new NO midi-send-receive message type 3. All banks are now visible in design mode 4. Basic fixes to design property pane for visual glitches 5. Add option to propagate MIDI min-max changes to Display Min/Max/Ticks Thanks for testing!
To test this app, open TestFlight on your iOS device using iOS 14.1 or later and install the update.