The totals in your shared event checklist keep getting overwritten, so you protect their formulas. That can help with collaboration. It does not make those cells private to you: someone who can read the file can still see its contents.
Check which kind of protection you selected
In Google Sheets on a computer, open Data → Protect sheets and ranges. A warning asks people to confirm an edit; it does not stop them. Restricting who can edit sets an editing permission. Choose deliberately, then try a harmless sample cell with the collaborator’s actual access rather than judging from the owner’s view.
Google explicitly says range protection is not a security measure. Hiding a tab is not a substitute: editors can reveal it, and hiding does not remove its data from the file. If protection is unavailable while editing an Office file, Google’s instructions point to converting it to Google Sheets; keep the original and check the converted copy.
Separate the information before sharing
Suppose attendees need the event timetable, while organizers need a separate list of personal arrangements. Create an attendee file containing only the intended information and give the planning file narrower access. A tab named Private inside the attendee file does not achieve that separation.
Label the input cells and explain which totals should stay untouched. Before sharing a copy or export, inspect that actual file again: included sheets, values and access can differ from the working version. Protection is useful for preventing editing mistakes; the sharing decision still determines who receives the information.