Not sure about all different databases but Postgres, for example, always stores datetimes in UTC and converts them back to a display timezone when outputting the values[0].

> For timestamp with time zone, the internally stored value is always in UTC (Universal Coordinated Time, traditionally known as Greenwich Mean Time, GMT). An input value that has an explicit time zone specified is converted to UTC using the appropriate offset for that time zone.

[0] https://www.postgresql.org/docs/current/datatype-datetime.ht...