Can I apply for an invention patent by combining several existing technologies into blank fields?

Of course, the application can be applied, but it will probably not be approved. According to what you said, it seems creative to achieve positive results in blank areas, but it also needs specific case analysis.

I think you should only apply for quick-frozen glutinous rice balls without applying for patents.

(1) Since every part exists, basically you don't need to describe every part in detail.

(2) It is not necessary to manufacture every part, and it is not necessary to apply for a patent in kind.

(3) If a number of existing technologies are combined, if the result is the sum of some functions, there is no unexpected effect, which actually does not meet the creative requirements, so it is difficult to obtain a patent right.

If these parts are combined, the function has been greatly improved, which is completely unexpected, and you can apply for a patent.