Hello Walaa,
yes, the default TypeConverter is exactly what I'm using for boolean value, but as you can see on the attached screenshot despite me even explicitly defining a length value of "1" for the "TinyInt" MySQL column in the Table Field Editor this "Max. length" is not set (and I also can't set it manually).
As a result the MySQL database TinyInt column gets defined with its maximum (display) length of "4" instead of the intended "1" for only boolean value.
And yes, I do know that internally the storage space needed for the column value stays always the same (it's still from type TinyInt after all), but it's good practice to define the length based on the actual need. This is even more true for DateTime field/column types where you only need the date part (and therefore restrict it to a length of "6").
Best regards and thanks again for your quick support on Christmas :-)
Andreas