There are many ways:
There’s also automatic tooltips that do this automagically. There’s also menu anchor widget that can pop something - afair, it respects screens boundary, I migth be wrong about the last one, though.
These are just for to preview the widget in the Designer. It gives you a reasonable idea of it will behave, so it’s easier to work with. Think of those modes as simulation.
This widget does not have a parent atm, but if you’re planning on placing it in a container like a 64x64 Size Box or Canvas that will enforce the Desired Size, you could set Custom On Screen to 64x64 as well. Now the widget will behave as if it was sitting in a restrictive parent even though it’s yet to be added there.