First note that the way you control gauges has changed in SU5. To get familiar with the new controls, please take a look at the release notes
It can happen that your keybinding profile has been changed. To reset this, go to Keybinding and reset your mouse to the Default profile to enable mouse control again. If this works you can change your own profile to include the correct bindings
Alternatively you can change back to the legacy control option via General Options-> Accessibilty → Cockpit Interactions System and select Legacy