I don’t believe this does what OP asked for. (“The cards still have his history of correct/incorrect answers, etc.” “How do I reset all my cards so they are like new?”)
Using Forget with “Reset repetition and lapse counts” does indeed set the card’s Reviews and Lapses counts to 0 and the due date to “New”, but that is all it does. It does not wipe out any of the other information found in the Info screen. (Edit: comparing Info display before and after a “forget and reset”, the lines for Due, Interval, Stability, Difficulty, Retrievability all disappear (I have turned FSRS on), whereas a value for Position newly appears, presumably as a result of “Restore original position where possible” being checked.)
So a “forgotten and reset” card with “Reviews = 0” will still have dates of First Review and Latest Review, plus the complete chronological log of all reviews from first to latest, with timestamps. (i.e., the previous user’s history mentioned by OP)
“Forgotten and reset” cards with this retained history can be found by searching for
is:new prop:reps=0 prop:lapses=0 introduced:999999
This incomplete resetting is not a recently introduced bug (or feature), because I have some cards that were “forgotten and reset” in August 2022, which are found with the above search. But I know I did another earlier mass “forget and reset” in January 2022, and those cards are not found with the above search, so I suppose they were indeed truly reset. Unfortunately, I’m not sure which versions of Anki I was using at the time.
I am pretty sure that FSRS analyzes the review logs to determine appropriate intervals? I turned on FSRS and have had “forgotten and reset” cards instantly jump to Hard = Maximum Interval, Good = Maximum Interval on the first subsequent review. So it seems there is a problem. (I might have been mistaken about that last part)