MacBook – Magic mouse two button click stopped working

• Double check that you don't have any stuck keys on your keyboard by testing all the keys, particularly the modifiers (shift, option, etc).
• Make sure there aren't any wizards, alerts, or dialogs hidden behind existing windows or in other spaces (this one gets me often, especially running the odd mix of programs I use daily).

Have you tried using MagicPrefs? You can use it to adjust the tracking speed, per their documentation.

Fine tuning tracking speed

MagicPrefs does not have available in the interface the fine tune tracking speed settings from the apple control panel, however they can be set manually by entering the next command in Terminal.app (change 0.3125 to your desired speed)

defaults write com.vladalexa.MagicPrefs TrackingMouse -float 0.3125

defaults write com.vladalexa.MagicPrefs TrackingTrackpad -float 0.3125

The Apple Tracking speed slider for the Magic Mouse and Magic Trackpad has 10 speed settings : 0.0, 0.125, 0.3125, 0.5, 0.6875, 0.875, 1.0, 1.7, 2.0, 3.0

The MagicPrefs Magic Mouse tracking speed slider has 10 speed settings : 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0

The MagicPrefs Magic Trackpad tracking speed slider has 10 speed settings : 0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0