For the majority of MMV devices, yes, the Cext pin can be grounded.
The Cext pin is internally grounded on many MMV's in TI's portfolio. Grounding this pin externally does not cause any negative impact on these devices. These include, but are not limited to, SN74LVC1G123, SN74LV123A, and SN74LV221A.
Some older devices should not have the Cext pin grounded.
The SN74221 and SN74LS221 are two examples in which the Cext pin should not be grounded externally, as described in the datasheet:
If you are looking to use a particular MMV that isn't covered above, please "Ask a related question" with the orange button at your top right. We can verify for you if the datasheet is unclear.
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