TIL you can't use both dataSourceBuilder.MapComposite<T> and NpgsqlConnection.GlobalTypeMapper.MapComposite<T> at the same time in #npgsql
docs: https://www.npgsql.org/doc/types/enums_and_composites.html?tabs=datasource

When you add mapping for composite type in GlobalTypeMapper - it replace datasource `UserTypeMapper` with global. Code here: https://github.com/npgsql/npgsql/blob/ab8e8db61617283603ac0350c1902222d710b92a/src/Npgsql/NpgsqlSlimDataSourceBuilder.cs#L423