Seems like the middle click isn't working anymore. Trigger works (tested with hud action).
Trigger it via trackpad top middle tap.
macOS: Sequoia (15.5)
BetterTouchTool: 5.538
That just sends a middle click, what happens afterwards is outside of BTT's control. What have you been using it for? You can e.g. test on Mouse Event Viewer
Sorry, It's an Arc issue, tested with Firefox where it works as I expected. It changes to cursor to
which sets the page to scroll automatically. The direction and speed can be influenced by up-/down movement on the trackpad.