.NET6 and DateTime problem. Cannot write DateTime with Kind=UTC to PostgreSQL type 'timestamp without time zone'

I have common problem.

Cannot write DateTime with Kind=UTC to PostgreSQL type 'timestamp without time zone' And I want to enable Legacy Timestamp behavoour as is documented here: https://github.com/npgsql/doc/blob/main/conceptual/Npgsql/types/datetime.md/

public MyDbContext(DbContextOptions<MyDbContext> contextOptions) : base(contextOptions)
        {
            AppContext.SetSwitch("Npgsql.EnableLegacyTimestampBehavior", true);
            AppContext.SetSwitch("Npgsql.DisableDateTimeInfinityConversions", true);
        }

But doesn't work. I still get same error. What I am doing wrong. Why legacy behaviour doesn't work?