Comments in Calc added date after update, and I don’t know how to change it back.
From what I read (and I tried it) that solution changes meta data from personal info to default info
What I take from bugzilla is: You can’t in 7.6 as it is a new feature to include this information now like Writer does before.
Exception are visible comments (I didn’t test).
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You may ask at bugzilla for further enhancement, to make this configurable by users, as comments in Calc are often used different in the programs (Revision control by editors in Writer vs explanation, what happens here in Calc), but it is hard to guess what purposes users also invented.