The feature you’re referring to is likely the ability of a (in .NET , typically System.Text.Json ) to read and parse a DateTimeOffset value that is formatted according to RFC 3339 (which is a subset of ISO 8601 used by JSON, gRPC, and many web APIs).
public DateTimeOffset? ParseDateTimeOffset(ReadOnlySpan<byte> json) utf8jsonreader datetimeoffset rfc 3339
When working with JSON data, DateTimeOffset can be used to deserialize date and time values from JSON. The feature you’re referring to is likely the
var options = new JsonReaderOptions
If you must parse a custom format without allocation, you typically have to convert to a Span<char> : json) When working with JSON data