Stretching a group when page lengthens?

I have a grey group with navigation links on the left, and a white group with repeating group on the right. The repeating group is able to grow in length, but the grey group can’t, so it looks wrong.

Are there any ways to make the grey group get longer when page lengthens?

You can use a Floating Group, anchored to Both Top and Bottom, with the height equal to the page height.
You might find this tutorial by Buildcamp useful: Dashboard layout | Tutorial - YouTube