If you take a look at your treeview you can see that the button selected: Group 2 is inside an another group called 1.BAAN FINDER Logo which is not a Frame
Group icon are a dotted square while frame would be a hashtag or a alignment icon (whether it’s a Frame or an Auto Layout)
You can make a frame above 1.BAAN FINDER Logo by selecting it and then pressing Ctrl+Alt+G on windows and Command+Option+G on mac
Once encapsulated in a frame you should be able to make link between your button and another frame