There is an option to lock some functions, but locking buttons and encoders is not included. You may want to check the several options of User Profiles in the "StudioLive_Series_III_OwnersManual_V6_EN_10062019", section 12.2 User Profiles and 12.2.3 Edit User Permissions.
I don't think that the buttons are too easy to activate. You need to push them actively, but not heavily. Would it help to "do" more things on the touchscreen? The whole Fat Channel is represented on the touchscreen, so selecting a function and turning that one encoder could take stress away from the indeed crowded physical Fat Channel area. Very often I use my left hand to mix/move the faders, so my right hand does all the "additional" work, including using a mouse (UC Surface/Capture/Studio One).
So, your request is to add a locking function to physical controls of the mixer (buttons, encoders, faders). The Profiles can solely handle DSP functions, so this might need a lot of DSP power, which the mixers probably do not have anymore.
But the idea is interesting... ;-) Good luck for this feature request!