cut fills area with white not transparency

[Sunny]

Hi,
I'm a beginner GIMP user - I use Linux Mint, GIMP 2.10.20

I opened a PNG image in Gimp. Then I used the rectangle selection tool to select an area I wanted to cut out. I cut it (Ctrl-X) and I tried  clicking CUT in the menu. Instead of having the area that was cut be transparent, GIMP fills it with white. 
How can I have it be transparent? like a hole

Thanks in advance

Sunny