It depends on the implementation and definition of “datetime” in whatever you’re working with. Taking Postgres as an example:

date: the concept of a calendar date (Your birthday)

timestamp: the concept of of a calendar datetime (You should get a new years kiss at 2022-01-01 00:00)

timestamptz: the concept of a precise moment in history (This comment was written at xxx time utc)

You can design a system where timestamps/datetimes are considered to be precise moments in time, utc, but that’s a matter of the impmentation you’re dealing with. Again, postgres does not assume timestamps as being in UTC (which has messed me up on more than one occasion).