How to resize image while maintaining aspect ratio and both frame/content

It is Shift+Command. But yo click that hamburger in the centre, so you select the image, not the container. Unselect everything, single-click the image so that you select the container, then Shift+Cmnd+ mouse to resize proportionally.

By @Peter Kahrel

Initially, I also thought that that's the issue. But after rewatching the video, I think there's indeed a problem with Shift not being applied. Otherwise OP wouldn't be able to make arbitrary resizing moves while resizing the object (whatever is being resized), which OP demonstrates in the beginning. When Shift is selected, any move of the mouse while resizing would still retain the aspect ratio of the object. Or am I misinterpreting what I see?