Conversion of pointer-to-pointer between derived and base classes?

If this was allowed, you could write this:

*bb = new Base;

And c would end up pointing to an instance of Base. Bad.

Pointers are virtual address. Normally you are responsible for what you do with it. Using msvc 2019. I can cast one to base, but not two:

example 1:

int p;
int *p1 = &p;
int **p2 = &p1; //OK

example 2:

struct xx {};
struct yy : public xx {};

yy p;
yy *p1 = &p;
xx **p2 = &p1; //Just a strange error

example 3:

struct xx {};
struct yy : public xx {};

yy p;
xx *p1 = &p; 
xx **p2 = &p1; //OK