Dedicated employee survey platforms separate responses from identities and suppress reporting below a minimum group size, so results for a team of four cannot be traced back to individuals. That threshold is the feature that matters, and it is rarely listed on a feature comparison page. Ask every vendor what the default minimum group size for reporting is and whether you can change it.
General form builders do not do this. They will happily report a team of three, and someone will eventually notice their answer was identifiable, after which honest answers stop. Whatever tool you use, state in the survey invitation who sees the raw responses and at what group size results get reported, and hold to it.