How to keep a frame in a UI ImageLabel proportional

In Size properties there is the relative size and the pixel absolute size. By default they always come with pixel absolute size. In this case you want to be using relative.
image

The image above has a 100x100 pixel size set. Size uses a UDim2 value to set the value. And UDim2 value looks like this:
({ScalarX, PixelX}, {ScalarY, PixelY})

Basically change the size using ScalarX and ScalarY to keep it responsive.

You may know more about Sizes right here:
https://developer.roblox.com/en-us/api-reference/property/GuiObject/Size

And this is a how to guide to responsiveness in Roblox: