From the “manual” in the web one can see that new and delete are not present in U++. Does this mean that ALL the widgets are created statically and therefore they are created at compilation time?
No.
What is going on is that heap is considered an implementation detail that should not be exposed in any interfaces.
Thus all U++ interfaces are designed to work without heap objects and that is why you do not see many new/deletes in the normal high-level code.
Also, for program logic, most cases where heap/new/delete was/is required in normal C/C++ programming are solved by using U++ containers.