Return date time as UTC

In Utilities folder, add DateTimeJsonConverter.cs

public class DateTimeConverter : JsonConverter<DateTime>
{
    public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        return DateTime.Parse(reader.GetString());
    }

    public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
    {
        writer.WriteStringValue(value.ToUniversalTime().ToString("yyyy-MM-ddTHH:mm:ssZ")); // "O" is the round-trip ISO 8601 format
    }
}

public class DateTimeOffsetConverter : JsonConverter<DateTimeOffset>
{
    public override DateTimeOffset Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        return DateTimeOffset.Parse(reader.GetString());
    }

    public override void Write(Utf8JsonWriter writer, DateTimeOffset value, JsonSerializerOptions options)
    {
        writer.WriteStringValue(value.ToUniversalTime().ToString("yyyy-MM-ddTHH:mm:ssZ"));
    }
}

In Program.cs

builder.Services.AddControllers().AddJsonOptions(options =>
{
    options.JsonSerializerOptions.Converters.Add(new DateTimeConverter());
    options.JsonSerializerOptions.Converters.Add(new DateTimeOffsetConverter());
});